Mean of values in the 1st column where the value in the second column is zero

I have data in a MAT file with 2 columns, the first column is length and the second column is 0 or 1.

eg: Length Y/N

      2.5       1

      3.2       0

How do I get mean of all values of first column where the value in second column is zero?

Answer 1

[Azzi Abdelmalek]

M=[2.5 1;3.2  0]
c1=M(:,1)
c2=M(:,2)
idx=c2==0
out=mean(c1(idx))

Answer 2

[Star Strider]

In one line:

S = mean(M(M(:,2)==0),1)

Answer 3

[Sid]

Thanks,that will do.