[R] subsetting a list of dataframes

[David Winsemius]

On May 17, 2011, at 7:13 PM, Lara Poplarski wrote:

> Thank you all, this is exactly what I had in mind, except that I  
> still have
> to get my head around apply et al. Back to the books for me then!
>

Read the lapply( ...)  call as:

"For every element in the object named `data`, send that element to a  
function that returns TRUE if its first dimension is greater than one,  
returns FALSE if its first dimension is one, and return nothing  
(actually a vector with zero elements) if it doesn't have a (first)  
"dim" attribute, and finally return the ordered collection of those  
values as a list which is assigned the name 'entries.with.nrows'. "


> Lara
>
> On Tue, May 17, 2011 at 2:41 PM, Jannis <bt_jannis at yahoo.de> wrote:
>
>> Have a look at lapply(). Something like:
>>
>> entries.with.nrows=lapply(data,function(x)dim(x)[1]>1)
>>
>> should give you a vector with the elements of the list that you  
>> seek marked
>> with TRUE.
>>
>> This vector can then be used to extract a subset from your list by:
>>
>> data.reduced=data[entries.with.nrows]
>>
>> Or similar....
>>
>>
>> HTH
>> Jannis
>>
>> --- Lara Poplarski <larapoplarski at gmail.com> schrieb am Di,  
>> 17.5.2011:
>>
>>> Von: Lara Poplarski <larapoplarski at gmail.com>
>>> Betreff: [R] subsetting a list of dataframes
>>> An: r-help at r-project.org
>>> Datum: Dienstag, 17. Mai, 2011 20:24 Uhr
>>> Hello All,
>>>
>>> I have a list of dataframes, and I need to subset it by
>>> keeping only those
>>> dataframes in the list that meet a certain criterion.
>>> Specifically, I need
>>> to generate a second list which only includes those
>>> dataframes whose number
>>> of rows is > 1.
>>>
>>> Could someone suggest how to do this? I have come close to
>>> what I need with
>>> loops and such, but there must be a less clumsy way...
>>>
>>> Many thanks,
>>> Lara
>>>
>>>    [[alternative HTML version deleted]]
>>>
>>> ______________________________________________
>>> R-help at r-project.org
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>>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained,
>>> reproducible code.
>>>
>>
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
Heritage Laboratories
West Hartford, CT