replacing the strings with a specific length in a cell

I want to replace the strings with lenght>=3 with 'm' in the second column of the following cell(without using a loop). So I want to get b from a. Any suggestion? thanks a lot

a =

    '1'    'aaaa'
    '2'    'a'   
    '3'    'aa'  
    '4'    'aaa'

b =

    '1'    'm' 
    '2'    'a' 
    '3'    'aa'
    '4'    'm'

Answer 1

[Oleg Komarov]

n   = 3;
idx = cellfun('prodofsize',a(:,2)) >= n;
a(idx, 2) = {'m'};

Note, however that cellfun is a concealed loop.

[FATEMEH]

Thank you Oleg!

[Jan]

+1: Thanks Oleg! I appreciate that I do not have to post my boring standard comments about the string commands for CELLFUN :-)