[R] taking rows from data.frames in list to form new data.frame?

[jctoll]

Dennis,

Thanks, the first example works perfectly.

> do.call(rbind, lapply(database, function(df) subset(df, Symbol == 'IBM')))

I haven't tried the second, but will look into plyr.

Thanks, again,

James



On Wed, Apr 20, 2011 at 6:36 PM, Dennis Murphy <djmuser at gmail.com> wrote:
> Hi:
>
> Perhaps you're looking for subset()? I'm not sure I understand the
> problem completely, but is
>
> do.call(rbind, lapply(database, function(df) subset(df, Symbol == 'IBM')))
>
> or
>
> library(plyr)
> ldply(lapply(database, function(df) subset(df, Symbol == 'IBM'), rbind)
>
> in the vicinity of what you're looking for? [Obviously untested for
> the usual reasons...]
>
> HTH,
> Dennis
>
> On Wed, Apr 20, 2011 at 4:13 PM, jctoll <jctoll at gmail.com> wrote:
>> Hi,
>>
>> I am having a problem figuring out how to extract a subset of rows.  I
>> have a list with 68 similar data.frames.  Each data.frame is 500 rows
>> by 5 columns.  I want to take one row from each data.frame based upon
>> the data in a particular column (i.e. it matches a symbol).  For
>> example:
>>
>>> str(database)
>> List of 68
>>  $ X2011.01.11:'data.frame':    500 obs. of  5 variables:
>>  ..$ Symbol    : chr [1:500] "MMM" "ACE" "AES" "AFL" ...
>>  ..$ Price     : num [1:500] 87.7 60.7 13.1 55.7 15.6 ...
>>  ..$ Shares.Out: num [1:500] 7.15e+08 3.39e+08 7.88e+08 4.71e+08 1.10e+08 ...
>>  ..$ Float     : num [1:500] 7.13e+08 3.38e+08 6.61e+08 4.60e+08 1.09e+08 ...
>>  ..$ Market.Cap: num [1:500] 6.27e+10 2.06e+10 1.04e+10 2.62e+10 1.72e+09 ...
>>  $ X2011.01.12:'data.frame':    500 obs. of  5 variables:
>>  ..$ Symbol    : chr [1:500] "MMM" "ACE" "AES" "AFL" ...
>>  ..$ Price     : num [1:500] 88.7 60.9 12.9 57.1 15.2 ...
>>  ..$ Shares.Out: num [1:500] 7.15e+08 3.39e+08 7.88e+08 4.71e+08 1.10e+08 ...
>>  ..$ Float     : num [1:500] 7.13e+08 3.38e+08 6.61e+08 4.60e+08 1.09e+08 ...
>>  ..$ Market.Cap: num [1:500] 6.34e+10 2.06e+10 1.02e+10 2.69e+10 1.68e+09 ...
>>  . . .
>>
>>> lapply(database, function(x) which(x == "IBM"))
>> $X2011.01.11
>> [1] 234
>>
>> $X2011.01.12
>> [1] 234
>>  . . .
>>
>>> lapply(database, function(x) x[which(x == "IBM"), ])
>> $X2011.01.11
>>    Symbol  Price Shares.Out    Float Market.Cap
>> 234    IBM 147.28   1.24e+09 1.24e+09 1.8297e+11
>>
>> $X2011.01.12
>>    Symbol Price Shares.Out    Float Market.Cap
>> 234    IBM 149.1   1.24e+09 1.24e+09 1.8524e+11
>>  . . .
>>
>> What I would like to do is create a new data.frame with 68 rows by 5
>> columns of data, perhaps using the old data.frame names as the new
>> row.names. I can get to the subset of data that I want, I just can't
>> get it from list form into one new data.frame.  Any suggestions?
>> Thank you.
>>
>> James
>>
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>