Determining probability mass function of random variable

Question

If we have a discrete random variable x and the data pertaining to it in X(n), how in matlab can we determine the probability mass function pmf(X)?

Answer 1

To add yet another option (since there are a number of functions available to do what you want), you could easily compute the pmf using the function ACCUMARRAY if your discrete values are integers greater than 0:

pmf = accumarray(X(:),1)./numel(X);

Here's an example:

>> X = [1 1 1 1 2 2 2 3 3 4];          %# A sample distribution of values
>> pmf = accumarray(X(:),1)./numel(X)  %# Compute the probability mass function

pmf =

    0.4000      %# 1 occurs 40% of the time
    0.3000      %# 2 occurs 30% of the time
    0.2000      %# 3 occurs 20% of the time
    0.1000      %# 4 occurs 10% of the time