R help - May 2010 - Idiomatic looping over list name, value pairs in R

Considering the python code:

for k, v in d.items(): do_something(k); do_something_else(v)

I have the following for R:

for (i in c(1:length(d))) { do_something(names(d[i]));
do_something_else(d[[i]]) }

This does not seem seems idiomatic. What is the best way of doing the
same with R?

Thanks.

Luis

Can you give an example of what the python code is supposed to do?

Some of us are not familiar with python, and the R code is not particularly
informative. You seem to encode information on both the values and the names of
the elements of the vector "d". If this is the case, why don't you
create a data frame (or a matrix) and call apply on the columns?

 

Christos
 
> Date: Tue, 4 May 2010 23:24:11 +0900
> From: globophobe@gmail.com
> To: r-help@r-project.org
> Subject: [R] Idiomatic looping over list name, value pairs in R
> 
> Considering the python code:
> 
> for k, v in d.items(): do_something(k); do_something_else(v)
> 
> I have the following for R:
> 
> for (i in c(1:length(d))) { do_something(names(d[i]));
> do_something_else(d[[i]]) }
> 
> This does not seem seems idiomatic. What is the best way of doing the
> same with R?
> 
> Thanks.
> 
> Luis
> 
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On 04/05/2010 10:24 AM, Luis N wrote:
> Considering the python code:
>
> for k, v in d.items(): do_something(k); do_something_else(v)
>
> I have the following for R:
>
> for (i in c(1:length(d))) { do_something(names(d[i]));
> do_something_else(d[[i]]) }
>
> This does not seem seems idiomatic. What is the best way of doing the
> same with R?
>   
You could do it as

for (name in names(d)) {
  do_something(name)
  do_something(d[[name]])
}

or

sapply(names(d), function(name) {
   do_something(name)
   do_something_else(d[[name]])
})

or

do_both <- function(name) {
  do_something(name)
  do_something_else(d[[name]])
}
sapply(names(d), do_both)

My choice would be the first version, but yours might differ.

Duncan Murdoch

Thank you. Your response was enlightening.

On Tue, May 4, 2010 at 11:38 PM, Duncan Murdoch
<murdoch.duncan at gmail.com> wrote:
> On 04/05/2010 10:24 AM, Luis N wrote:
>>
>> Considering the python code:
>>
>> for k, v in d.items(): do_something(k); do_something_else(v)
>>
>> I have the following for R:
>>
>> for (i in c(1:length(d))) { do_something(names(d[i]));
>> do_something_else(d[[i]]) }
>>
>> This does not seem seems idiomatic. What is the best way of doing the
>> same with R?
>>
>
> You could do it as
>
> for (name in names(d)) {
> ?do_something(name)
> ?do_something(d[[name]])
> }
>
> or
>
> sapply(names(d), function(name) {
> ?do_something(name)
> ?do_something_else(d[[name]])
> })
>
> or
>
> do_both <- function(name) {
> ?do_something(name)
> ?do_something_else(d[[name]])
> }
> sapply(names(d), do_both)
>
> My choice would be the first version, but yours might differ.
>
> Duncan Murdoch