How to count in arrays?

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Evelyn
Evelyn 2014-11-17
评论： John D'Errico 2014-11-17
Let's say I have two arrays
apple = [1 2 3 4 5 6 7 8];
pear = [2 3 1 2 7 6 1 8];
I want to compare these arrays and count how many items in pear are bigger than the item at the same place in apple. How would I do this?
  1 个评论
the cyclist
the cyclist 2014-11-17
编辑：the cyclist 2014-11-17
Sounds like homework. Here are a few hints:
  • There is "greater than" operator in MATLAB, which will operate on vectors
  • There is also an operator that will sum over a vector
  • There is a docsearch command that will search the documentation

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Manoj
Manoj 2014-11-17
x=sum(pear>apple);
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John D'Errico
John D'Errico 2014-11-17
While this correct, I recall that it will be slightly faster to use nnz instead of sum.
x = nnz(pear > apple);
The difference will be small unless the arrays are significantly large.
pear = round(rand(1,1e7)*10);
apple = round(rand(1,1e7)*10);
timeit(@() sum(pear > apple))
ans =
0.03888
timeit(@() nnz(pear > apple))
ans =
0.023221

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