For-loop,string variables, and the $-operator

Hi all,

First time poster, so sorry if I commit some breech of posting etiquette.

My problem is as follows. I have a data frame where each column represents
a category and the individual data points in each category are binary
responses (in this case they are actually 1's and 0's). What I want to
extract are the counts for each category and put them in a vector. To do
that I used the following:

cats<-c("cat1","cat2", "cat3", ...)
c()->counts
for(j in cats){
                     append(counts, sum(data$j)) -> counts
                       }

However, the 'counts' object only contains 0's after the script runs:

counts
[1] 0, 0, 0, ....

  After replacing various elements in the script to isolate what the issue
is, I've discovered the problem stems from  "data$j". Is there a reason
using a variable with the subset operator is bad?

Thanks,
Allan

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