[R] From data frame to list object

[David Winsemius]

On Jan 31, 2011, at 1:56 PM, Bogaso Christofer wrote:

> Thanks David for this reply. However if my data frame has only 2  
> columns
> then it is working fine. It is not working for a general setting:
>
> dfrm <- data.frame(x=rnorm(18), y=rep(c("a", "b", "c"), each=6),
> z=rep(c("x", "y", "z"), each=2))
> tapply(dfrm[,1], dfrm$y, c) # this is working fine
>
>> tapply(dfrm[,c(1,3)], dfrm$y, c)  # this is giving error!
> Error in tapply(dfrm[, c(1, 3)], dfrm$y, c) :
>  arguments must have same length
>
> Can you please help me how to modify that?

You will need to specify what you goals are. What to you want to  
happen to those two columns referred to by dfrm[, c(1,3)]? It's  
possible that split() may be the answer, but clarify the goals first.  
You should provide an example that represents the complexity of the  
task.

>
> Thanks,
>
> -----Original Message-----
> From: David Winsemius [mailto:dwinsemius at comcast.net]
> Sent: 31 January 2011 23:26
> To: Bogaso Christofer
> Cc: r-help at r-project.org
> Subject: Re: [R] From data frame to list object
>
>
> On Jan 31, 2011, at 1:03 PM, Bogaso Christofer wrote:
>
>> Dear all, let say I have following data frame:
>>
>>
>
>> dfrm <- data.frame(x=rnorm(18), y=rep(c("a", "b", "c"), each=6))  >
> tapply(dfrm$x, dfrm$y, c) $a [1]  0.9711995  1.4018345 -1.4355713  
> -0.5106138
> -0.8470171 [6]  1.1634586
>
> $b
> [1] -0.8058164  0.4977112  1.1556391  0.8158588  0.2549273 [6]   
> 3.0758260
>
> $c
> [1]  0.437345128 -0.415874363  0.003230285 -0.737117910 [5]   
> 1.247972964
> 0.903001077
>
>
>>
>>> data.frame(x=rnorm(18), y=rep(c("a", "b", "c"), each=6))
>>
>>             x y
>>
>> 1  -1.072152537 a
>>
>> 2   0.382985265 a
>>
>> 3   0.058877377 a
>>
>> 4  -0.006911939 a
>>
>> 5  -2.355269051 a
>>
>> 6  -0.303095553 a
>>
>> 7   0.484038422 b
>>
>> 8   0.733928931 b
>>
>> 9  -1.136014346 b
>>
>> 10  0.503552090 b
>>
>> 11  1.708609658 b
>>
>> 12 -0.294599403 b
>>
>> 13  1.239308497 c
>>
>> 14  0.754081946 c
>>
>> 15 -0.237346858 c
>>
>> 16 -0.051011439 c
>>
>> 17 -0.618675146 c
>>
>> 18  0.537612359 c
>>
>>
>>
>>> From this data frame I want to create a "list" of length 3, where
>>> each
>> element of this list will be a vector corresponding to the value of  
>> y.
>> For example, 1st element will be all "x" values corresponding to the
>> "y=a", and similarly the other elements of this list. Can somebody
>> point me how to do this without having some "for" loop?
>>
>>
>>
>> Thanks and regards,
>>
>>
>> 	[[alternative HTML version deleted]]
>>
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>> and provide commented, minimal, self-contained, reproducible code.
>
> David Winsemius, MD
> West Hartford, CT
>

David Winsemius, MD
West Hartford, CT