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# Finding the values right after and right before some values in a matrix

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mr mo on 6 Nov 2017
Commented: Guillaume on 8 Nov 2017
Hi. Suppose I have the matrix A of size (m*n).
A = [12 44
93 43
128 44
145 41
180 41
220 40
280 40];
also I have the vector V e.g.
V = [13 20 70 90 95 100 102 110 129 130 145 158 170 185 190 200 207 220 270 280 285 290];
I want to find which one of the rows of matrix A based on its first column values is right after and right before the values of vector V, and if one of the values of the first column of matrix A is equal to the values of vector V, I want to find that row.
For example :
A(2,1) is right before V(5) and V(6) and V(7) and V(8)
A(3,1) is right after V(5) and V(6) and V(7) and V(8)
and in case of equality I want to find this
A(4,1) = V(11)
A(5,1) = V(18)
A(7,1) = V(20)
In other words, I want to find exactly which members of vector V are between which members of first column of matrix A with their indices like this :
V(1) and V(2) and V(3) and V(4) is between A(1,1) and A(2,1)
Thanks for your help.
##### 2 CommentsShowHide 1 older comment
mr mo on 6 Nov 2017
I am looking for this. For example
V(1) and V(2) and V(3) and V(4) is between A(1,1) and A(2,1)

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### Answers (2)

KL on 6 Nov 2017
Edited: KL on 6 Nov 2017
res = find(V>A(1,1) & V<A(2,1))
for all elements,
res = arrayfun(@(x,y) find(V>x & V<y), A(1:end-1,1), A(2:end,1),'uni',0)
##### 9 CommentsShowHide 8 older comments
mr mo on 7 Nov 2017
Suppose I want to find that only V(10)=130 is lying between which two members of A(:,1). How can I do this process to have the out cell array like your last code?
And in case of equality how can I have the out cell array like the case of inequality? Thanks a lot.

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Guillaume on 7 Nov 2017
An alternative method that does not involve loops (or arrayfun) but is not necessary faster than KL's:
comp = abs(A(:, 1) - V);
comp(A(:, 1) > V) = inf;
[~, beforeVidx] = min(comp, [], 2);
isequaltoV = A(:, 1) == V(beforeVidx)';
%for display only:
table(A, beforeVidx, isequaltoV)
##### 4 CommentsShowHide 3 older comments
Guillaume on 8 Nov 2017
Same issue, same solution, use bsxfun:
comp(bsxfun(@gt, A(:, 1), V)) = inf;

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