R help - Oct 2010 - SApply versus for loop for list of data.frames

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.

Thanks,
Chris

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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

-- 
David.

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.