How to select specific rows with a certain range/certain value in another row?

Two simple questions I haven't managed to find the right answers for:

1: I have a 1x1 cell called "Data". This 1x1 cell contains a 1x100 cell, so basically the 100th data would be Data{1,1}{1,100}. In the analysis I only want to include the data until cell 90. I've tried it with

    Data = Data{1,1}{1,1:90}

which doesn't seem to work.

2: I have a 10x8 double. What I'd like to calculate is the mean value of all the values in row 2 for all data which value in their row 4 is "5".

Any help would be appreciated.

Answer 1

[Christopher Berry]

Pinga,

1. To get Data as a 1x90 cell array, use the following code:

Data = Data{1}(1:90)

There are two ways to refer to the elements of a cell array. Enclose indices in smooth parentheses, (), to refer to sets of cells—for example, to define a subset of the array. Enclose indices in curly braces, {}, to refer to the text, numbers, or other data within individual cells.

2. Assume that your 10x8 double data is in A

mean(A(2,A(4,:)==5));

Here, A(4,:)==5 returns a logical vector of each column containing a '5' in row 4, which you then use to logically index into row 2 columns.

Hope that helps.

[Pinga]

Christopher, thank you very much!

1. In the script, I refer a few times to

   Data{1,1}{1,1}(1,1)

Therefore, I want to keep the format of the new Data. With

    Data = Data{1}(1:90)

I directly get a 1x76 cell. Is there a way to get a format like this: {1,1}{1,1}... until {1,1}{1,76}?

2. My fault, I meant columns, not rows. I've tried it with

    mean(A(A(:,4)==5),2)

Insted of getting one mean value, I get now a (:,1) matrix, containing zeros.

Thank you in advance!

[Christopher Berry]

Ok, I think I understand what you are asking, but if I get it wrong let me know.

1. What you want sounds like

Data = {Data{1,1}(1:90)}

This way your size of data is 1x1 cell, whose 1st cell contents are a 1x90 cell array.

2. When you say "I meant columns, not rows", I am going to guess your question should have been "What I'd like to calculate is the mean value of all the values in column 2 for all data which value in their corresponding row column 4 is "5".

And it looks like that is what you are doing, but with misplaced (). Try this instead

mean(A(A(:,4)==5,2))

Notice the lack of ) after "5" and the double )) at the end of the line.

[Pinga]

Super, that was a really great help - thanks a lot! Although having worked with Matlab for a few months now, it appears to me, I'm just adapting way too slowly on this whole new programming stuff (such misplaced () keep me troubleshooting and frustrating quite some time).