How to traverse table row based on sets

Let's say that I have a table in an excel spreadsheet that looks like this (based off of real GPS data, but for the sake of this question, all of these are just random numbers ):

|Set number| PRN | X-coordinate | y-coordinate | z-coordinate ...

| 1 | 17 | 24715 | -1470517 | 223695 |

| 1 | 17 | 24715 | -1470517 | 223695 |

...

| 2 | 17 | 24715 | -1470517 | 223695 |

| 2 | 17 | 24715 | -1470517 | 223695 |

So I know that I can read in the data using the build in MATLAB command:

gpsdata = readtable('spreadsheet.xlsx')

I also know I can loop through the table by row using the command:

for row = 1:height(gpsdata)

However, more specifically, I want to loop through all the table based off the set numbers in each row. One snag is that the number of set numbers varies. Sometimes there will be 8 rows of set 1, other times there will be 9 rows of set 2, etc.

My specific aim is to do specific operations on each of the sets. Looking at the table, normally there is a different PRN for each satellite. That means each measurement is a different satellite. The set is just a way to acknowledge that it is measuring the same thing. For example, the set 1s will have about 8 different satellites all measuring whatever is at set 1. However, each of the satellites will have a different measurement. My goal is to take all the measurements and use iterative least squares to estimate the exact measurement. However, that involves getting measurements from each of the different satellites within each row of the set.

Is there a way that I could loop through based off each of the set numbers to make sure that the ones that I am using are the same for each set? That is, what is the best way to operate on all the rows with set data 1s, then operate on all the data with set 2s, etc.?

While I could do each set manually, I feel as though there is a better, more programmatic way to approach this.

Thanks for your time and help in advanced! I really appreciate it!

[jonas]

Why do you need to use a loop? What is the desired output? I suspect that you want to use the set number as a grouping variable, in which case grpstats or findgroups/splitapply would be much better than looping.

[billyjthorton]

I certainly don't need to use a loop, but just thought of it as a logistic programmatic tool (e.g. for each set...). However, I don't know much about those other commands? How would those work in a table?

[jonas]

In general, you can group sets of data based on some grouping variable and perform some operation on each group. The function grpstats is specifically for calculating statistics of groups from a table (e.g. mean, std etc etc..), it's quite flexible.

You can read about those function sin the documentation. If you descibe what your specific aim is here, then you could get some concrete advice.

[billyjthorton]

My specific aim is to do specific operations on each of the sets. Looking at the table, normally there is a different PRN for each satellite. That means each measurement is a different satellite. The set is just a way to acknowledge that it is measuring the same thing. For example, the set 1s will have about 8 different satellites all measuring whatever is at set 1. However, each of the satellites will have a different measurement. My goal is to take all the measurements and use iterative least squares to estimate the exact measurement. However, that involves getting measurements from each of the different satellites within each row of the set. Does that make more sense?

As an aside, I looked into the functions and they don't work quite out of the box. That is, I can't do grpstats(gpsdata) or findgroups(gpsdata). I think grpstats is closer to what I would like to achieve, but when I do something like grpstats(gpsdata,1) I get the error "Unrecognized variable name 'Set Number' ". Any assistance you could provide given the table set up as shown above?

[Walter Roberson]

Can you attach a sample dataset?

[billyjthorton]

I think I attached it above. And on this post. Can you see it?

[jonas]

It seems like you could use either grpstats or findgroups with a custom function for your least square estimate. Actually they are very much alike.

You can try working with arrays instead, e.g.:

 grpstats(gpsdata.var,gpsdata.set,'mean')

will output the set-mean of the specific variable. The statistic (third argument) can be a custom function.

[billyjthorton]

So what would be an example for "var" and "set" in this case. I guess I'm not sure how to properly break it into arrays?

[jonas]

grpstats([T.X_coordinate,T.Y_coordinate],T.SetNumber,'mean')

Will give you the mean coordinates of the sets. The columns included in the first argument must be numeric or logical. The function also accept table inputs, which is sometimes cleaner. If you input a table, then the output is also a table.

grpstats(T(:,1:4),'SetNumber','mean')

I suspect you want to use a custom function. Is the equation you'd want to employ different or consistent for each set?

[billyjthorton]

That makes sense. However, I'm still a bit confused. What is 'SetNumber'? If I reference any of the strings in the table it can't recognize the variable (e.g. 'X-coordinate'). Does that mean I make an additional column vector for that particular piece? e.g.

grpstats(gpsdata, 'SetNumber', 'mean')

still errors. I'll write a custom function for the ILS stuff - it should be pretty consistent. The one thing that I'm thinking about is how to write it in such a way that it's adaptable no matter how many are in each set.

[jonas]

SetNumber is the name of the variable that you want to use as grouping variable. The syntax is as follows>

grpstats(x,groupingvariable,stats)

how you specify the groupingvariable depends upon the class of x. If x is a table, then groupingvaraible is a variable name. When importing with readtable, "SetNumber" was assigned automatically as variablename to my 1st column, so that's where that came from. You can get a list of the variable names like this (T is your table):

T.Properties.VariableNames

If x is instead a matrix, then groupingvariables is also a matrix (or vector), with the same amount of rows as the matrix.

Either way, x cannot include non-numerical columns, and will return an error if your table includes a column of strings. You can take a subset of your table by using braces, e.g. T(:,1:5), will pass the first 5 columns. This subset must include the groupingvariable and should not include any column that is non-numeric, because how do you calculate the mean of a string?

Going to get some sleep, will check in tomorrow morning. Cheers.

[billyjthorton]

It took me some time, but I realized I was having trouble with what you mention above would be the issue. I'm running into non-integer values that are causing the problem. However, it seems to be a hurdle I can't quite fix.

For example:

grpstats(gpsdata(1:110,1:17), gpsdata.Var1)

This produces: "Unrecognized variable name 'Set Number'". As you can see in the attached test data, that string is present. However, even if I shift it and do:

grpstats(gpsdata(2:110,1:17), gpsdata.Var1)

The exact same error is present. Even if I take only the numeric data, copy it into another spreadsheet and try to process it with something like:

grpstats(gpsdata(2:108,1:17), gpsdata.x1)

I still get an error: "Duplicate variable name: 'x0'".

I can't quite group the data successfully. In doing more research on some MATLAB functions, I learned about the find function. It seems possible to use the "find" function to find all rows where the Set Number is equal to each number (1-12) and grouped the data that way. However, that seems to take in only numeric values as well. Given that when I use readtable to bring in the spreadsheet, it's in table format, I can't seem to convert it (e.g. table2array) into a version that is actually usable by find either.

[jonas]

grpstats(gpsdata(1:110,1:17), gpsdata.Var1)

"Unrecognized variable name 'Set Number'"

There is no string called 'Set Number' in that line of code. Also, Set Number (with a blank) is not a valid variable name, so I'm not surprised it did not work anyway. Check your variable names in MATLAB, as readtable parse them when reading from excel.

"As you can see in the attached test data, that string is present. However, even if I shift it and do:"

grpstats(gpsdata(2:110,1:17), gpsdata.Var1)

The above is the exact same as the previous line. I don't understand what you tried.

"Even if I take only the numeric data, copy it into another spreadsheet and try to process it with something like:"

grpstats(gpsdata(2:108),1:17), gpsdata.x1)

Something wrong with this line of code. It makes no sense, the braces are placed incorrectly.

Regarding the find function, there are indeed many ways to group and work with your data. The find function (or logical indexing) could be useful would you choose to move forward with a for loop. I suggested the above approaches as they are quite effecient and elegant ways to deal with grouped data, without using a loop. If you have experience with for loops, then perhaps that is the way to go. I do not understand why you'd want to find strings, as your grouping variable is a double.

Unless you give a more detailed account of how you want to process the groups, then I do not know what more advice to give you. As of right now, we are stuck on issues related to syntax and not the actual problem in question.

[billyjthorton]

I apologize, I made a mistake with the braces on the third command. If you look closely between the first and second command, you'll noticed that it has been shifted by one to avoid a row. I provided the exact data I'm dealing with. Look at the original question as well as a post above and you'll see an attached spreadsheet with the data. I shifted the data I was looking at by a row to avoid "Set Number", which, while not in the code, is in the data set. As for the third command, I thought I was clear on what it was doing. It was designed to run in the above dataset, without any of the strings (just grabbing the block of data that I was going to use anyways), but it's more or less just a modified version of the first two and no success on that front either. I firmly believe I should be able to do this without trying to remove the strings and just select the data that I want to use as a sub-matrix.

I apologize, I don't know how much more clear to be? I have written a more detailed explanation of exactly what I want to do. Alas, I will try again:

I would like to capture the grouping of all the data under set "1", then do a capture of all the data under set "2" and so on and so forth. Once I have other a sub array or indices, I can then take the data and perform operations. Particularly, go row by row and extract the GPS data to perform geolocation using an ILS method. Does that help answer what you are looking for?

Is there any way you'd be willing to open up the data I sent and be able to provide more specific help? I'm really trying to learn, but I'm really struggling using this data set.

[jonas]

I'll write a more elaborate response in a bit. For now, just two comments. First:

grpstats(gpsdata(2:108,1:17), gpsdata.x1)

Wrong syntax. If you insert a table, then the grouping variable arg should be a string describing the variable name. If you want the column gpsdata.x1 as your grouping variable, then the correct syntax is:

grpstats(gpsdata(:,1:17), 'x1')

This should work as long as each of the 17 first columns contain numerical data only, and one variable is named x1.

Second, I assumed you had imported the table correctly but realized now that this is not the case. Follow Guillaumes advice. If it still does not work, then use the 'range' argument of readtable to skip the first line of the sheet. As for now, all your variables are imported as strings, as the first row in your table is a string. Note that it doesn't matter that you write:

gpsdata(2:108,1:17)

each column is still interpreted as strings.

Answer 1

[Guillaume]

It's unclear what problem you are actually facing with Jonas' examples. As Jonas says, you can easily use any of the grouping functions that work with tables. Not having the stats toolbox, I use varfun and rowfun. Here is a rowfun example to works with your attached excel file. I use it to calculate the mean 3D distance (from origin) of the satellites in each group. Adapt as required:

%function to use with rowfun. Defined as anonymous function here. Could be an m file instead
%takes 3 column vector inputs, x,y and z coordinates. Return a scalar
func = @(x, y, z) mean(sqrt(x.^2 + y.^2 + z.^2));
%import file
opts = detectImportOptions('GPS_data.xlsx');  %works better at figuring out that the header is on row 2
satdata = readtable('GPS_data.xlsx', opts);
%apply function to each set of satellites
rowfun(func, satdata, 'GroupingVariables', 'SetNumber', 'InputVariables', {'X_coordinate', 'Y_coordinate', 'Z_coordinate'}, 'OutputVariableNames', 'distance')

[billyjthorton]

Thank you for your answer, I really appreciate it! I apologize if I wasn't learn on @jonas's answer. All I did were these two commands:

gpsdata = readtable('GPS_data.xlsx')
grpstats(gpsdata(2:110, 1:17), gpsdata.Var1)

And it spat out the error:

Unrecognized variable name 'Set Number'

which comes from that second row that you pointed out.

I'm not sure on your answer, what the difference is between GroupingVariables and SetNumber. Would you be able to do a practical example with set '1' data so I can better see an example of operating on set 1 data? It doesn't have to be fancy, maybe just disp() the X-Coordinate and Y-Coordinate. I apologize to be a bother, but it would be a huge help.

[Guillaume]

I would recommend that you read the documentation of varfun

I cannot help with grpstats. As I said, I don't have the required toolbox and have never used the function.

"what the difference is between GroupingVariables and SetNumber" . 'GoupingVariables' is the name of the parameter as documented, 'SetNumber' is the actual value of the parameter and is the name of the variable you want to use for grouping.

Would you be able to do a practical example

The code I've given with my answer works perfectly well with the example file you've provided. How more practical do you want? have you tried it?

[billyjthorton]

I apologize, I made a slight error on my implementation. However, I was referring specifically to the function. For example running:

%import file
opts = detectImportOptions('GPS_data.xlsx');  %works better at figuring out that the header is on row 2
satdata = readtable('GPS_data.xlsx', opts);
%apply function to each set of satellites
rowfun(func, satdata, 'GroupingVariables', 'SetNumber', 'InputVariables', {'X_coordinate', 'Y_coordinate', 'Z_coordinate'}, 'OutputVariableNames', 'distance')

function out=func(x,y,z)
disp(x,y,z)
end

Produces the error:

Not enough input arguments.

Error in group_test>func (line 28)
disp(x,y,z)

Error in group_test (line 25)
rowfun(func, satdata, 'GroupingVariables', 'SetNumber', 'InputVariables', {'X_coordinate',
'Y_coordinate', 'Z_coordinate'}, 'OutputVariableNames', 'distance')

Do I have to format my function in a specific way?

[Guillaume]

You need to pass a function handle to rowfun, so @func, not func (in my example, func was already a function handle to an anonymous function).

You're still going to get an error since your function defines an output that gets nothing assigned to it and since disp doesn't take 3 arguments.

I'm not sure what you're trying to do with your function. It needs to return something. If you want to know what x, y, z are going to contain, it's simple. The function will be called once for each group (defined by unique values in the GroupingVariables SetNumber). Each time x will be the column vector of X_coordinates matching the set number, y the column vector of Y_coordinates, etc.

At this point, it would be simpler if you told us exactly what operation you want to perform on your table.

[billyjthorton]

Each of the coordinates of each set will be used to feed an ILS algorithm. More particularly, it would be good to create a variable for each set of x, y and z coordinates that can be used to feed the algorithm.

Here is a program that I wrote that does it for a set amount of coordinates:

% Given measurements
x_true = [1132049; -4903445; 3905453; 85000]' % meters
x_init = [0;0;0;0]

% SV locations
sv1=[15764733;-1592675;21244655]
sv2=[6057534;-17186958;19396689]
sv3=[4436748;-25771174;1546041]
sv4=[-9701586;-19687467;15359118]
sv5=[23617496;-11899369;1492340]
sv6=[14540070;-12201965;18352632]

% x_old values
num_it = 5
x_old=zeros(num_it+1,4)
% sigma
sd=5;

% Generate Measurements
rho1=sqrt((sv1(1)-x_true(1))^2 + (sv1(2)-x_true(2))^2 + (sv1(3)-x_true(3))^2) + x_true(4)+sd*randn(1)
rho2=sqrt((sv2(1)-x_true(1))^2 + (sv2(2)-x_true(2))^2 + (sv2(3)-x_true(3))^2) + x_true(4)+sd*randn(1)
rho3=sqrt((sv3(1)-x_true(1))^2 + (sv3(2)-x_true(2))^2 + (sv3(3)-x_true(3))^2) + x_true(4)+sd*randn(1)
rho4=sqrt((sv4(1)-x_true(1))^2 + (sv4(2)-x_true(2))^2 + (sv4(3)-x_true(3))^2) + x_true(4)+sd*randn(1)
rho5=sqrt((sv5(1)-x_true(1))^2 + (sv5(2)-x_true(2))^2 + (sv5(3)-x_true(3))^2) + x_true(4)+sd*randn(1)
rho6=sqrt((sv6(1)-x_true(1))^2 + (sv6(2)-x_true(2))^2 + (sv6(3)-x_true(3))^2) + x_true(4)+sd*randn(1)

% Estimation
for i = 1:5

   rho1_hat=sqrt((sv1(1)-x_init(1))^2 + (sv1(2)-x_init(2))^2 + (sv1(3)-x_init(3))^2) + x_init(4)
   rho2_hat=sqrt((sv2(1)-x_init(1))^2 + (sv2(2)-x_init(2))^2 + (sv2(3)-x_init(3))^2) + x_init(4)
   rho3_hat=sqrt((sv3(1)-x_init(1))^2 + (sv3(2)-x_init(2))^2 + (sv3(3)-x_init(3))^2) + x_init(4)
   rho4_hat=sqrt((sv4(1)-x_init(1))^2 + (sv4(2)-x_init(2))^2 + (sv4(3)-x_init(3))^2) + x_init(4)
   rho5_hat=sqrt((sv5(1)-x_init(1))^2 + (sv5(2)-x_init(2))^2 + (sv5(3)-x_init(3))^2) + x_init(4)
   rho6_hat=sqrt((sv6(1)-x_init(1))^2 + (sv6(2)-x_init(2))^2 + (sv6(3)-x_init(3))^2) + x_init(4)

   % partial derivatives

   h1=[ -[(sv1(1)-x_init(1)) (sv1(2)-x_init(2)) (sv1(3)-x_init(3))]/(rho1_hat-x_init(4)) 1]
   h2=[ -[(sv2(1)-x_init(1)) (sv2(2)-x_init(2)) (sv2(3)-x_init(3))]/(rho2_hat-x_init(4)) 1]
   h3=[ -[(sv3(1)-x_init(1)) (sv3(2)-x_init(2)) (sv3(3)-x_init(3))]/(rho3_hat-x_init(4)) 1]
   h4=[ -[(sv4(1)-x_init(1)) (sv4(2)-x_init(2)) (sv4(3)-x_init(3))]/(rho4_hat-x_init(4)) 1]
   h5=[ -[(sv5(1)-x_init(1)) (sv5(2)-x_init(2)) (sv5(3)-x_init(3))]/(rho5_hat-x_init(4)) 1]
   h6=[ -[(sv6(1)-x_init(1)) (sv6(2)-x_init(2)) (sv6(3)-x_init(3))]/(rho6_hat-x_init(4)) 1]

   h=[h1;h2;h3;h4;h5;h6]

   % x_init - x_hat
   dy=[rho1-rho1_hat;rho2-rho2_hat;rho3-rho3_hat;rho4-rho4_hat;rho5-rho5_hat;rho6-rho6_hat]

   %x_hat = x_init + inv(H.'*inv(R)*H)*H.'*inv(R)*(y_1 - h)
   dx=inv(h'*inv(sd^2)*h)*h'*inv(sd^2)*dy
   x_init=x_init+dx

   x_old(i+1,:)=x_init'

end

% Show Results
format long
iteration_results=x_old

Now I just need to implement it so that all the SVs will be each of the coordinate pairs and then proceed into the loop as normal

[jonas]

Just to clarify.

SV1-6 are x,y,z-coordinates from 6 different satellites? If that's so, then you will have to learn to not use indexed variable names (which is never a good idea), because you are about to have a variable number of coordinate triplets.

Other than that it doesn't appear to be too much work. You should clean up the script, make it into a function, and then apply it in your grouping operation. Perhaps you can edit the script and indicate the values that will change when you vary the number of input triplets.

[billyjthorton]

Yes, that is correct. What is the alternative to indexed variable names in this case? Leverage each as a function of the loop variable? What would be the loop variable in this case?

[Guillaume]

I'm sorry but Ew! One rule that you need to put into practice immediately: numbered variables are always the wrong approach. sv1 should be sv(1), sv{1} or sv(1, :) or something similar. And every time you're repeating more or less the same lines of code, you're doing it wrong. Computers are very good at repeating things, let them do the work.

Your script, written in proper matlab:

% Given measurements
x_true = [1132049, -4903445, 3905453, 85000]; % meters
x_init = [0, 0, 0, 0];
% SV locations
sv = [15764733, -1592675,   21244655
      6057534,  -17186958,  19396689
      4436748,  -25771174,  1546041
      -9701586, -19687467,  15359118
      23617496, -11899369,  1492340
      14540070, -12201965,  18352632];
% x_old values
num_it = 5;
x_old = zeros(num_it, 4);
% sigma
sd=5;
% Generate Measurements
rho = sqrt(sum((sv - x_true(1:3)) .^ 2, 2)) + x_true(4) + sd*randn(1);
% Estimation
for i = 1:num_it
   rho_hat = sqrt(sum((sv - x_init(1:3)) .^ 2, 2)) + x_init(4);
   % partial derivatives
   h = [-(sv - x_init(1:3)) ./ (rho_hat - x_init(4)), ones(size(sv, 1), 1)];
   % x_init - x_hat
   dy = rho - rho_hat;
   %x_hat = x_init + inv(H.'*inv(R)*H)*H.'*inv(R)*(y_1 - h)
   dx = inv(h'*inv(sd^2)*h)*h'*inv(sd^2)*dy;
   x_init = x_init + dx.';
   x_old(i, :) = x_init;
end

Also note the warnings in the editor. I'm fairly certain you shouldn't be using inv but that's outside of my domain of expertise.

What I'm missing is what that script has to do with the table. What are the inputs and outputs of that scripts and how do they match the table?

Answer 2

[jonas]

Method 1 - grpstats

For the sake of simplicity, let's use only the first 5 columns in this example.

%%Import data
opts = detectImportOptions('GPS_data.xlsx'); 
T = readtable('GPS_data.xlsx', opts);
T = T(:,1:5);

T =

109×5 table

    SetNumber    PRN    X_coordinate    Y_coordinate    Z_coordinate
    _________    ___    ____________    ____________    ____________

        1        17      2.4716e+06     -1.4705e+07       2.237e+07 
        1         6     -5.2026e+06     -2.5099e+07      6.9419e+06 
    ...

Continuing...

%%Split and apply custom function
grpstats(T,'SetNumber',@func);

function out=func(x)
  out=mean(x);
end

You can write your own function, just remember that the input, x, is always a column vector containing one group and a single variable. This is of course limiting, because you cannot perform complex operations on multiple variables in your function, or at least I do not know how. For this, it is better to use another method.

Method 2 - findgroups/splitapply

Read the data just like before, but transform the table into an array.

A=table2array(T);

Now, split the dataset in groups and perform some operation with all 4 variables (excluding Set Number) at once.

%%First column is grouping set
G = findgroups(A(:,1));
out1 = splitapply(@func,A(:,2:end),G);

function out1=func(vars)
vars
%%perform some calculations here
end

You can see that I have written out the variables passed to the custom function. What is nice here is that you can process all four variables in the same function. You can pass multiple outputs back to the main script if you so desire, however each output should be scalar.

vars =

   1.0e+07 *

    0.0000    0.2501   -1.4700    2.2370
    0.0000   -0.5196   -2.5091    0.6975
    ...

I've never used rowfun personally but I suppose it's very similar to the second method.

[Guillaume]

I've never used rowfun personally but I suppose it's very similar to the second method

Yes, it's just simpler as I've shown in my answer! ?

With your particular example, you'd have to use varfun instead:

varfun(@func, T, 'GroupingVariables', 'SetNumber')

It's actually much closer to your first method.

[billyjthorton]

Thank you so much for your answer - this was really helpful! I followed what you said on the second iteration (in a separate test file "group_test.m") and your usage of splitapply seems to error out:

opts = detectImportOptions('GPS_data.xlsx')
gpsdata = readtable('GPS_data.xlsx', opts)
gpsdata = gpsdata(:,1:17)

A = table2array(gpsdata)

G = findgroups(A(:,1))

out1 = splitapply(@func,A(:,1:end),G)

function out1=func(vars)
vars
end

Error using splitapply (line 129) Applying the function 'func' to the 1st group of data generated the following error:

Output argument "out1" (and maybe others) not assigned during call to "group_test>func".

Produces the error:

Error using splitapply (line 129)
Applying the function 'func' to the 1st
group of data generated the following
error:

Output argument "out1" (and maybe
others) not assigned during call to
"group_test>func".

Error in group_test (line 9)
out1 = splitapply(@func,A(:,1:end),G)

Is there a different way I should be using splitapply?

[jonas]

Well, I suppose you want to write an actual function before running the script. The error message says that the function output (called out1) is not assigned any value, which is true because you did not specify any equation. There is even a comment in the function that says

%%perform some calculations here

Write something here, like

 function out1=func(vars)
   xcoord = vars(:,2)
   ycoord = vars(:,3)
   zcoord = vars(:,4)
   out1 = xcoord+ycoord+zcoord;
 end

Whatever the equation, it will be performed groupwise.

[jonas]

@Guillaume: Awesome. I will probably have to switch over to rowfun and varfun instead. If nothing else, it's one line of code instead of two (findgroups/splitapply) :)

[billyjthorton]

Ooooh that makes sense. So "vars" is the group of coordinates (and other GPS data stuff). I really like that.

However, one weird thing that has popped up - it calls for an anonymous function?

Error using splitapply (line 129)
The function 'func' returned a non-scalar value when applied to the 1st group of data.

To compute nonscalar values for each group, create an anonymous function to return each
value in a scalar cell:

  @(x1){func(x1)}

Error in group_test (line 9)
out1 = splitapply(@func,A(:,1:end),G)

Why would it do that?

[jonas]

I know this is a lot to take in. If you're just starting to learn matlab, this may be a few levels above what you should be doing (such as learning about different classes, basic operations and loops). I hope you don't feel discouraged.

As I wrote above:

" You can pass multiple outputs back to the main script if you so desire, however each output should be scalar."

You cannot pass a matrix as output. Each output has to be scalar (a single value). You can pass multiple outputs though, in which case you just add

 function [out1,out2,out3...]=func(vars)
   %%some calculations
   out1=1;
   out2=2;
   out3=3;
 end

will pass three outputs back to the main script, all of which have to be scalar. Maybe you could solve this by passing cell arrays as output, but that would certainly only complicate things for you.

To summarize, do all your calculations for each group inside of the function, then pass the results to the main script for futher analysis.

[billyjthorton]

Ah, that makes sense. Thank you for your help and patience! It follow at least from the error code, but the issue seems to be in the function itself. I followed your code earlier:

function out1=func(vars)
xcoord = vars(:,2)
ycoord = vars(:,3)
zcoord = vars(:,4)
out1 = xcoord + ycoord + zcoord 
end

With still the same scalar error. But isn't out1 a scalar in this case already? Additionally, right now it only provides a loop through the first group. Theoretically, should it be looping through all of them? I believe this scalar error is getting in the way, but I was trying to make sure what to expect.

[jonas]

Ugh, thats not scalar. Scalar is a single element. That is a matrix. Poor example from my end.