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I have an array S 440x120 in dimensions. There is another array T 440x1.

I need to append say rows of S to another array T1 based on the following conditions

  1. The rows appended must be from index say 100 to 200 in S.
  2. Only those rows with T(100:200)==1 should be included. This means that if T(100)=0 then S(100,:) should not be included and if T(101)=1 then S(101,:) should be included.

I tried using the following but it failed due to obvious reasons as it includes from the first index and not from the 100th.

T1=S(T(100:200)==1,:);

Is there a shorter way of doing this in matlab apart from writing a whole loop? Thanks for your answers.

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2
  • When you say "add all columns of S to another array", do you mean add each column of S or add the sum of all columns of S? Commented Nov 13, 2013 at 9:56
  • Each column of S is what I mean. Commented Nov 13, 2013 at 9:57

3 Answers 3

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You almost have it. You only need to add an offset to the numeric (not logical) indices: 

N = 100;
M = 200;
result = S(N-1+find(T(N:M)==1),:);
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5 Comments

Uh Oh! Ill try that. Could you please comment the code so I can understand what it actually does? :P
Thanks! Why the sum though? I think I got my answer from this though. Will try it out.
@SohaibI You said "add those colummns"... by "add" did you mean "sum" or simply "include"?
I don't mean add as in addition! Ill make the edit in my question. I mean add as in append to that.
I have already written that as an answer in my question. This does not work. It includes rows from the first index in S and not from the 100th index.
2

How about T1=S([zeros(99,1); T(100:200)]==1,:);?

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4 Comments

Not sure if the zeros should be a row or column matrix. Either this or [zeros(1,99) T(100:200)]. You use the zeros to ignore the first 99 elements of S and start at index 100.
it should be 101. Ill try it out and report back.
Subscript indices must either be real positive integers or logicals?
@SohaibI Make sure you don't have a typo, it seems to work fine.
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Here you go:

idx = find(T==1);
idx = idx(idx>=100 & idx<=200);

S(idx,:)
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3 Comments

You could save the first 99 ==1 comparisons... :-)
Can't mark all answers correct unfortunately :P @LuisMendo I think you took that find() function idea from here ;) Thanks for all the help.
@SohaibI Not really :-) When you want to add an offset to a set of indices, the indices have to be in numeric form, not in logical form; and find does just that. What took me some time was to understand the question ;-)

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