finding most common letter in a cell array

If I have a cell array

x={'overcomplete';'phellandrene';'phenanthrene';'pneumatocele';'pneumonocele'
'preintercede';'preinterfere';'pseudocumene';'pseudosphere';'spermatocele'}

how do I find the most common letter in x that does not appear in say we have a string &nbsp y='aer' &nbsp so say the highest occurring letter in x is a we ignore 'a' because it appears in y and find the second highest occurring number in x say its 'e' we ignore 'e' because it appears in y and we find the next one we keep doing this until the highest occurring letter in x does not appear in y and we use that as the highest occurring letter

Answer 1

[per isakson]

Try

x = {'overcomplete';'phellandrene';'phenanthrene';'pneumatocele';'pneumonocele'
     'preintercede';'preinterfere';'pseudocumene';'pseudosphere';'spermatocele' };
y = 'aer';
xpr = regexprep( y, '(\w{1})(?=\w)', '$1\|' );  % remove the letters of y
cac = regexprep( x, xpr, '' );
str = cat( 2, cac{:} );                         % concatenate all words
asc = double( str );                            % convert to ascii-numbers
edges       = [min(asc):1:max(asc)];
[ n, bin ]  = histc( asc, edges );
ixm         = find( n == max(n) );
fprintf(['highest occurring letters in x, which doesn''t appear in y, are ' ...
    ,    '"%s" with %i occurrences\n'],  char(edges(ixm)), n(ixm(1)) )

outputs

highest occurring letters in x, which doesn't
appear in y, are "np" with 11 occurrences

Answer 2

[Stephen23]

This is very simple with mode:

>> v = +[x{:}];
>> char(mode(v(~any(bsxfun(@eq,v,y(:))))))
ans = n

Note: if there are multiple characters that occur the same number of times, then mode returns the one with the lowest character value.