R help - Nov 2012 - 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

	[[alternative HTML version deleted]]

Hello,

It's bad to use the subset operator '$' because you don't have a
column
named 'j'. Use data[[j]]

Hope this helps,

Rui Barradas
Em 27-11-2012 21:22, Allan Schwade escreveu:
> 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
>
> 	[[alternative HTML version deleted]]
>
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