How can I find index of element in array? (2024)

Often logical indexing is more efficient, so you might only need this:

Bear in mind that if the number occurs more than once in the vector, the result returned is a vector containing the indices of all occurrences. If you want the index of just the first occurrence of the number, insert 1 as the second argument in find:

Doesn't answer the question

Henrik, yes it does, as I understand the question. Why do you say it doesn't?

What difficulty do you find with James' answer? He showed the find() function, which is the function defined to locate the places where a condition occurs.

If you need to have the exact question answered more clearly, "but did Matlab doesn't have build-in similar function?" then the answer to that is "NO, MATLAB does not have a built-in function in which you can provide only the array name and the value, and MATLAB will return all the indices of the value in the array."

Note: if you only need to know the first location, then you can also use

result will be 0 if 5 is not present in x.

The function find() is useful as far as matrices (2-D tensors) are concerned. I cannot, however, find a useful function for nd-arrays where, for instance, the index could be an array on its own. See example below:

M = reshape(1:24, [2,3,4]);

indices = index_finder(M==20); % indices = vector of indices

It would be very useful if there was a function which worked for tensors of any dimensionality.

@Ehsan Partovi I couldn't agree with you more; this is a problem I seem to run into often, and here is my solution:

The only drawbacks are the reuirement that you know how many dimensions. YOu can get around this with CSLs like so: