Reputation: 71

converting 1 matrix into multiple matrices

I have a rather large matrix in which column 1 list times in 100ths of a sec (e.g. 3000 = 30s) and in column 2 are event codes (e.g. 1 = start of trial, 2 = start of response, 4 = end of trial). I have used this larger matrix to determine all sorts of indices. However, now I need to compute an indice on a trial by trial basis (i.e. based on the values between 1 and 4 which repeat for a total of 60 times. An example array consisting of 3 trials is below:

What I want to do is populate a new array for each 1 & 4 pair, for example, in this array of 3 x 1 & 4 pairs the first trial would consist of the following

Tarray_1 = [0,682,987,2586,2593,2598, 2601, 2602, 2605, 2607, 2608,2635, 2636, 5546; 1,2,3,2,3,2,3,2,3,2,3,2,3,4];

Is there any easy or straight forward to do this? I've spent the last few days try to use for loops and the find command to determine the indices of every 1 in order to create new arrays. Does anyone have any suggestions as to what I could do?

Upvotes: 2

Answers (3)

chappjc

Reputation: 30579

Given an n-by-2 matrix M, here is an easy way with just two commands:

>> trialStartEnd = [find(M(:,2)==1) find(M(:,2)==4)]

trialStartEnd =

     1    14
    15    24
    25    31

>> T = arrayfun(@(x,y) M(x:y,:)',trialStartEnd(:,1),trialStartEnd(:,2),'uni',0)

T = 

    [2x14 double]
    [2x10 double]
    [2x7  double]

Each trial has it's own array in a cell of T.

Upvotes: 4

Marcin

Reputation: 238309

Here is one way, if I understand correctly, of ding this:

A = [0       1;
682     2;
987     3;
2586    2;
2593    3;
2598    2;
2601    3;
2602    2;
2605    3;
2607    2;
2608    3;
2635    2;
2636    3;
5546    4;
7321    1;
7826    2;
7900    3;
7901    2;
7902    3;
9481    2;
9730    3;
9877    2;
10319   3;
10431   4;
11158   1;
11361   2;
11376   3;
12209   2;
12267   3;
13547   2;
14159   4];




% all even codes
evenCodes = A(:, 2);


% find positions of valus 4 in the even cods
[indx c] = find(evenCodes == 4);


% just append 0 to the idx array
newIdxOfFours = [0, indx'];


% cell cointaining Tarrays, e.g. outCell{1} is Tarray_1
TarrayCell = {};

for i = 1:length(newIdxOfFours) - 1

    % find starting and ending index/row for each trial
    startIdx = newIdxOfFours(i) + 1;
    endIdx = newIdxOfFours(i+1);

    TarrayCell{end + 1} = A(startIdx:endIdx, :)';


end

TarrayCell{1}
TarrayCell{2}
TarrayCell{3}

>> 
ans =

           0         682         987        2586        2593        2598        2601        2602        2605        2607        2608        2635        2636        5546
           1           2           3           2           3           2           3           2           3           2           3           2           3           4


ans =

        7321        7826        7900        7901        7902        9481        9730        9877       10319       10431
           1           2           3           2           3           2           3           2           3           4


ans =

       11158       11361       11376       12209       12267       13547       14159
           1           2           3           2           3           2           4

Upvotes: 0

David

Reputation: 8459

I wrote this code, which may work with your code, however depending on what you need these matrices to do, having them in cells may be a hassle. But in the absence of other answers this should do the trick. I copied the big matrix you gave and called it A.

[F,I]=find(A(:,2)==4);
T=cell(1,sum(I));
T{1}=A(1:F(1),:);
for j=2:sum(I)
    T{j}=A(F(j-1)+1:F(j),:);
end

This makes a cell array of matrixes, T, and you can get any matrix out by using eg: T{1}, or access a particular element with eg: T{1}(2,1).

Edit: This assumes that the matrix starts with a 1, and that another 1 always follows a 4. Chappjc's answer is probably better.

Upvotes: 0

converting 1 matrix into multiple matrices

Answers (3)

Related Questions