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Hey everyone,

I'm having a problem figuring out how to get the sum of each column conditional upon the value in the column. I've pasted a subset of my data below and basically for each column I want to know how many "I"s are in each column. I used the following line of code:
apply(status,2,function(x) {sum(x==I,na.rm = TRUE)})

The output tells me that there are 0 "I"s in each column, but it's clear that is not true. Any help would be greatly appreciated.

Thanks

2010 2011 2012
1 A A A
2 A I I
3 A A A
4 U U U
5 A A A
6 I I I
7 U I I
8 A U A
9 I A U
10 I I I