Question

I have an array of 100K structs. I am listing below the contents of one such struct:

Iteration:1

BlockID:86

The BlockID can have values between 1 and 100. I want to find out the count of occurrences of BlockID. For eg.: BlockID “1” occurred 25 times; BlockID “98” occurred 58 times and so on.

I looked online and tried the options mentioned in these links, but could not get a solution:
Matlab: Count number of structs that have a specific content
how to count unique elements of a cell in matlab?
Matlab: How to calculate how many unique strings are stored in the cell?

Answer 1

You can use arrayfun and count_unique (count_unique is not an official function – it’s from the matlab central file exchange and can be found here):

ids= arrayfun(@(x)x.BlockID, struct1);
[vals, counts] = count_unique(ids);

NB: As pointed out by rody_o (though he/she missed the fact that the indexing is unnecessary) there is an alternative way to concatenate the, ids, namely

ids = [struct1.BlockID];

Alternatively you could create your own count_unique function if you wished,

function [counts, uns] = count_unique(ids)
uns= unique(ids);
counts = arrayfun(@(x)sum(ids == x), uns);