[R] Subset a list

[Chuck Cleland]

Doran, Harold wrote:
> I have a data frame of ~200 columns and ~20,000 rows where each column
> consists of binary responses (0,1) and a 9 for missing data. I am
> interested in finding the columns for which there are fewer than 100
> individuals with responses of 0. 
> 
> I can use an apply function to generate a table for each column, but I'm
> not certain whether I can subset a list based on some criterion as
> subset() is designed for vectors, matrices or dataframes.
> 
> For example, I can use the following:
> tt <- apply(data, 2, table)
> 
> Which returns an object of class list. Here is some sample output from
> tt
> 
> $R0235940b
> 
>     0     1     9 
>  2004  1076 15361 
> 
> $R0000710a
> 
>     0     9 
>     2 18439 
> 
> $R0000710b
> 
>     0     1     9 
>  3333  3941 11167 
> 
> tt$R0000710a meets my criteria and I would want to be able to easily
> find this instead of rolling through the entire output. Is there a way
> to subset this list to identify the columns which meet the criteria I
> note above?

How about this?

newdf <- mydf[,colSums(mydf == 0) < 100]

> Thanks,
> Harold
> 
> 
> 
> 
> 	[[alternative HTML version deleted]]
> 
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Chuck Cleland, Ph.D.
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