You can use the "histogram" command in Matlab to obtain an approximate probability density (pdf) function for your data. For example if the vector X contains your data, type "histogram(X)" in Matlab command window and it plots an approximate probability density function for the data contained in X.
Note that more data gives more precise pdf for the data.
Mahmood is right, althogh, the function you are looking for is "hist(x)". Y=hist(X,N) returns the data of X separated into N equally spaced containers and specifies each quantity in the Y array.