[R] SApply versus for loop for list of data.frames

[David Winsemius]

On Oct 12, 2010, at 12:33 AM, David Winsemius wrote:

>
> On Oct 12, 2010, at 12:16 AM, rivercode wrote:
>
>>
>> Hi,
>>
>> I am trying to find the total number of rows for a list of  
>> data.frames and
>> want to know if there is a better way than using a loop like:
>>
>>> df = { list of data.frame with varying number of rows...each one  
>>> has a
>> column called "COL" }
>>> r = 0
>>> for (i in 1:length(df)) {
>> + r = r + length(n[[i]]$CON)
>> + }
>>> r
>> 6000123   <----  number of rows.
>
>
> r <- lapply(df, NROW)
> r

Rather:

sum(unlist(r))  # or
sum(sapply(df,NROW))

sum

>
> -- 
> David.