finding highest values in string

say I have a string x='asdqweqweasdddasdaaaaaaaaasdeeeeeer' and another string y='aed' how do I find the letter that occurs in x the most as long as its not in y so for example the most common letter in x is 'a' we ignore 'a' and find the second most common letter in x that does not appear in y which is 'e' we ignore 'e' because it appears in x we do this until we find the highest occurring letter in x that does not appear in y

Answer 1

[Mohammad Abouali]

x='asdqweqweasdddasdaaaaaaaaasdeeeeeer';
y='aed';

uniqueCharsNotInY=unique(x(~ismember(x,y)));

charCount=arrayfun(@(c) sum(x==c),uniqueCharsNotInY');

mostRepeatedCharNotInY=uniqueCharsNotInY(charCount==max(charCount))
mostRepeatedCharNotInY =

s