Question

I have to count how often a certain string is contained in a cell-array. The problem is the code is way to slow it takes almost 1 second in order to do this.

    uniqueWordsSize = 6; % just a sample number
    wordsCounter = zeros(uniqueWordsSize, 1);
    uniqueWords = unique(words); % words is a cell-array

    for i = 1:uniqueWordsSize
        wordsCounter(i) = sum(strcmp(uniqueWords(i), words));
    end

What I’m currently doing is to compare every word in uniqueWords with the cell-array words and use sum in order to calculate the sum of the array which gets returned by strcmp.

I hope someone can help me to optimize that…. 1 second for 6 words is just too much.

EDIT: ismember is even slower.

Answer 1

You can drop the loop completely by using the third output of unique together with hist:

words = {'a','b','c','a','a','c'}
[uniqueWords,~,wordOccurrenceIdx]=unique(words)
nUniqueWords = length(uniqueWords);
counts = hist(wordOccurrenceIdx,1:nUniqueWords)

uniqueWords = 
    'a'    'b'    'c'
wordOccurrenceIdx =
     1     2     3     1     1     3
counts =
     3     1     2