summing elements of an array until a value appears

I'm trying to execute a for loop that looks at permutations of a set and sums all the elements until a specific element 'k' is reached.

rather than sum(line(1:k)) i need effectively sum(line(1:'k')) but inputting that exactly doesn't work. Any ideas?

if sum(line(1:k))>=q && (sum(line(1:k))-k)<q

[Turlough Hughes]

I don't get what you mean by sum(line(1:'k')) vs sum(line(1:k)), can you clarify?

[Turlough Hughes]

You wouldn't need a loop, you could just use cumsum and find your value in the output.

[Thomas Gvero]

Sorry I wasn't very clear. I am basically trying to sum every permutation of an array up to and including a particular element (not always the same index each time). For example, if I was summing up to 2, and my permutations were:

1,2,3

1,3,2

2,1,3

then my sums would go up to the number 2 not the second element. The sums would be 3,6,2 repectively.

[Thomas Gvero]

this is running in a wider for loop of a function so i need it to output exactly what i need each time which is why i need the second loop

Answer 1

[Mohammad Sami]

a = [1 1 1 2 3 4 2];
i = find(a==2,1,'first');
if ~isempty(i)
    val = sum(a(1:i));
else
    val = sum(a);
end

Answer 2

[the cyclist]

Here is one way.

% Inputs
inputVector = [5 4 3 2 1];
inputValueToFind = 2;

% Find the location of the index
idxEnd = find(inputVector==inputValueToFind,1);

% Sum up to that index
sum(inputVector(1:idxEnd))

Answer 3

[Turlough Hughes]

Say your array is called data:

q=2;
data = [1 2 3; 1 3 2; 2 1 3; 1 0 3; 1 2 2]; % Includes rows without any values = q, and repeated q.

You could then get the cumulative sum of values up to the first occurence of q in each row as follows:

[ ~,k ] =  max(data == q,[],2);   % Index for first column equal to q in each row. 
k(~any(data == q,2)) = 0          % Case for rows that have no values == q.
for c = 1:numel(k)
    csums(c,1) = sum( data(c,1:k(c)) );
end

Here, data == q is a logical array of all values in data that are equal to q. Taking the max along each row will return the "first" index for a given row in data being equal to q. The second line accounts for cases where no values are equal to q.