How do I get the least used character in the text file ?

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Tony
Tony 2015-4-25
评论： Jan 2015-4-26
a= textread('GreatExpectations.txt','%c');
[m]=length(a);
most_used_letter=char(mode(0+a))

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Mohammad Abouali
Mohammad Abouali 2015-4-25
编辑：Mohammad Abouali 2015-4-26
%Sample text; equivalent to your a
txt='this is a sample text.';
uniqueChars=unique(txt(isletter(txt)));
charCount=arrayfun(@(c) sum(txt==c), uniqueChars);
% Now printing results
fprintf('Char count\n');
fprintf(' %c %d\n',[uniqueChars;charCount])
fprintf('\nThe least Used Characters are:\n')
fprintf('%c\n',uniqueChars(charCount==min(charCount)))
fprintf('\nThe most Used Characters are:\n')
fprintf('%c\n',uniqueChars(charCount==max(charCount)))
Once you run it you well get this:
Char count
a 2
e 2
h 1
i 2
l 1
m 1
p 1
s 3
t 3
x 1
The least Used Characters are:
h
l
m
p
x
The most Used Characters are:
s
t
  2 个评论
Mohammad Abouali
Mohammad Abouali 2015-4-26
编辑：Mohammad Abouali 2015-4-26
You are welcome.
In larger texts, when you are sure that all characters are used you can remove uniqueChars=unique(txt(isletter(txt))); and then modify the next line form
charCount=arrayfun(@(c) sum(txt==c), uniqueChars);
to
charCount=arrayfun(@(c) sum(txt==c), char([65:90 97:122]));
You have to be sure that all characters are used though. Otherwise, those characters that are not used would be returned as the least used characters.
Also if upper/lower case are not important; then once you are done reading the text file do this:
txt=lower(txt);
and in this case if you decided to use the second form you need char(97:122) instead of char([65:90 97:122]);
If this has answered your question, I appreciate it if you accept the answers.

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per isakson
per isakson 2015-4-26
编辑：per isakson 2015-4-26
Here is a code based on histc
ffs = 'GreatExpectations.txt';
fid = fopen( ffs );
buf = fscanf( fid, '%1c' );
fclose( fid );
letters only
ascii = double( upper( buf ) );
ascii( ascii<double('A') | ascii>double('Z') ) = [];
ascii_ranges = ( double('A') : double('Z') );
[ ascii_counts, ~ ] = histc( ascii, ascii_ranges );
bar( ascii_ranges, ascii_counts, 'histc' )
min_val = min( ascii_counts );
ix_min = find( ascii_counts == min_val );
fprintf( 'The letters, %s, each appears %d time(s)\n' ...
, char('A'+ix_min-1), min_val )
it prints
The letters, JQZ, each appears 1 time(s)
&nbsp
Regarding char('A'+ix_min-1) see 'ABC'-'A' Considered Harmful

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