matlab plot histogram indicating sum of each character inside a file

Question

I have 400 files, each one contains about 500000 character, and those 500000 characters consists only from about 20 letters. I want to make a histogram indicating the most 10 le

Answer 1

Note: This answers the original version of the question (the data consists of 10 letters only; a histogram is wanted). The question was completely changed (the data consists of about 20 letters, and a histogram of the 10 most used letters is wanted).

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If the ten letters are arbitrary and not known in advance, you can't use hist(..., 10). Consider the following example with three arbitrary "letters":

h = hist([1 2 2 10], 3);

The result is not [1 2 1] as you would expect. The problem is that hist chooses equal-width bins.

Here are three approaches to do what you want:

1. You can find the letters with unique and then do the sum with bsxfun:

   letters = unique(part(:)).';             %'// these are the letters in your file
   h = sum(bsxfun(@eq, part(:), letters));   %// count occurrences of each letter
   

2. The second line of the above approach could be replaced by histc specifying the bin edges:

   letters = unique(part(:)).';
   h = histc(part, letters);
   

3. Or you could use sparse to do the accumulation:

   t = sparse(1, part, 1);
   [~, letters, h] = find(t);
   

As an example, for part = [1 2 2 10] either of the above gives the expected result,

letters =
     1     2    10
h =
     1     2     1