Inserting data of one matrix into another

If I have a vector a

0
0
1
1
0 
0

and a vector b

5
6

and I want to input the data of b into the nonzero elements of a (which will always be together and matching the dimensions of b), so that vector c reads

0
0
5
6
0
0

What is an easy way to do this? Thank you!

Another example that it needs to work for:

a    b          c
_    _          _
0    4          0
0    8          0
1    3   ---->  4
1    7          8
1               3 
1               7

Answer 1

[Adam]

a(a ~= 0) = b

[Chris]

That's right where my thinking is, but it's not changing anything about a after that line of code! If I display a right after the line you provided, it is still 0's and 1's.

[Adam]

It works fine when I try it! And also for your other example. Are you sure you typed it exactly the same way?

[José-Luis]

No, it shouldn't, given the provided data. Please post the code you are using.

[Star Strider]

Interesting. It works for me, replacing the appropriate elements of ‘a’ with the elements of ‘b’.

[Chris]

Well it doesn't matter to me if it creates a new vector or overwrites the original data of vector "a" - let's just change "a" for now since that's what I stated originally.

Here's my actual code

    d = S \ P    % Vertical vector of -0.89955, -0.001057

    U = all(K)'; % Vertical vector of 0 0 1 1 0 0

    U(U ~= 0) = d % Displays vertical vector of 0 0 1 1 0 0

[Adam]

Ah well, your vector is logicals, not doubles! That makes it more, well...logical...in terms of syntax!

Since you don't care if it is in the same vector or a different vector then

c(a) = b;
c = c';

should work, inserting your own variable names as appropriate. There's probably a slightly neater way of getting back to a vertical vector. You can pre-allocate c as:

c = zeros(size(a));

if you prefer or if you don't care whether your result is a row vector or a column vector you can leave off the c' line. I don't generally like code myself though that switches between column and row vectors mid-way through a calculation.

[José-Luis]

This should work:

 d = [-0.8; -0.001];
 U = [0 0 1 1 0 0]';
 U(U~=0) = d

If it doesn't, then d and U (or both) probably don't contain what you think they do. Also, the common lingo for "vertical vector" is "column vector".

[Chris]

Adam, pre-allocating c and then using

c(a) = b;

worked great, thanks so much for the help everyone.

[José-Luis]

Please accept the answer of it solved your problem.

[Shane Hagen]

I have a slightly different issue maybe someone can help?

I have a matrix [signal] of 315954x64 of signal data. In another matrix [FFlash] (155520x1) there is logical 1 or 0 depending on an activation

I have categorized the signal matrix to obtain a matrix [FFsignal] (155520x64) of data when there is an activation

To graph I need matrices of similar dimensions so I wanted to insert the categorized data into a matrix of zeros of size (315954x64)

For example the first group of activation is in rows 631-654 and when categorized I have data for those time points. I want to add this data to a matrix of zeros in the same time points if possible. Therego, zeros until 631-654 and so on through the set. Please help!

Answer 2

[Stephen23]

MATLAB's powerful indexing makes this easy, if we use logical indexing:

>> a = [false;false;true;true;false;false];
>> b = [5;6];
>> c = zeros(size(a));
>> c(a) = b
c =
     0
     0
     5
     6
     0
     0

And the same for the second example:

>> a = [false;false;true;true;true;true];
>> b = [4;8;3;7];
>> c = zeros(size(a));
>> c(a) = b
c =
   0
   0
   4
   8
   3
   7

[Shane Hagen]

any insight on my issue stephen? I would really appreciate any help.

[Stephen23]

"I have a slightly different issue..." → ask a new question.

[Shane Hagen]

I posted the question :Inserting data into matrix of zeros from another matrix.

Answer 3

[LUI PAUL]

try simple

a=[0;0;1;1;0;0];

b=[5;6];

p=find(a>0);

a(p)=b

a =

     0
     0
     5
     6
     0
     0

[James Tursa]

You have totally missed the issue. The 1's & 0's vector "a" is logical. So your scheme doesn't work. E.g.,

>> a = logical([0 0 1 1 0 0]);
>> b = [5 6];
>> p = find(a>0);
>> a(p) = b
a =
     0     0     1     1     0     0

[LUI PAUL]

its not mentioned 'logical'.Chris said only vector....logical may not be used....

[James Tursa]

Go to Adam's answer. Read the 5th and 6th comments by Chris and Adam. They clearly show that the fundamental issue is that "a" is logical, and Adam posts a solution for this that works when "a" is logical.

[LUI PAUL]

for logical a,...try this

a = logical([0 0 1 1 0 0]);

a=double(a);

b = [5 6];

p = find(a>0);

a(p) = b

a =

     0     0     5     6     0     0

what do you think @James will it work?

[James Tursa]

Yes.