[R] Extracting column name in apply/lapply

[Sundar Dorai-Raj]

Nick Desilsky wrote:
>   Hi,
>    
>   any good trick to get the column names for title() aside from running lapply on the column indexes?
>    
>   Thanks
>    
>   Nick.
>    
>   apply(X[,numCols],2,function(x){
>   nunqs <- length(unique(x))
>   nnans <- sum(is.na(x))
>   info <- paste("uniques:",nunqs,"(",nunqs/n,")","NAs:",nnans,"(",nnans/n,")")
>   hist(x,xlab=info) 
>   # --> title("???")
>   })
> 
> 
>  		
> ---------------------------------
> 
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This is where a for loop is much more useful (and readable):

for(i in numCols) {
   nunqs <- length(unique(X[, i]))
   nnans <- sum(is.na(X[, i]))
   ## `n' is missing from this example
   info <- 
paste("uniques:",nunqs,"(",nunqs/n,")","NAs:",nnans,"(",nnans/n,")")
   hist(X[, i],xlab=info)
   title(colnames(X)[i])
}

HTH,

--sundar