[R] Help with ddply/summarize

[John Posner]

> -----Original Message-----
> From: David L Carlson [mailto:dcarlson at tamu.edu]
> Sent: Friday, November 14, 2014 10:25 AM
> To: John Posner; 'r-help at r-project.org'
> Subject: RE: Help with ddply/summarize
> 
> I think this is what you want:
> 
> > MyVar <- 1:10
> > MyVar
>  [1]  1  2  3  4  5  6  7  8  9 10
> > mean(MyVar)
> [1] 5.5
> > txt <- "MyVar"
> > mean(txt)
> [1] NA
> Warning message:
> In mean.default(txt) : argument is not numeric or logical: returning NA
> > mean(get(txt))
> [1] 5.5
> 

Got it.  I was also pointed to get() by David Winsemius. Thanks to both Davids!

-John


> 
> -------------------------------------
> David L Carlson
> Department of Anthropology
> Texas A&M University
> College Station, TX 77840-4352
> 
> 
> 
> 
> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
> On Behalf Of John Posner
> Sent: Thursday, November 13, 2014 5:32 PM
> To: 'r-help at r-project.org'
> Subject: [R] Help with ddply/summarize
> 
> I have a straightforward application of ddply() and summarize():
> 
>    ddply(MyFrame, .(Treatment, Week), summarize,
> MeanValue=mean(MyVar))
> 
> This works just fine:
> 
>    Treatment     Week MeanValue
> 1    MyDrug  BASELINE      5.91
> 2    MyDrug    WEEK 1      4.68
> 3    MyDrug    WEEK 2      4.08
> 4    MyDrug    WEEK 3      3.67
> 5    MyDrug    WEEK 4      2.96
> 6    MyDrug    WEEK 5      2.57
> 7    MyDrug    WEEK 6      2.50
> 8    Placebo BASELINE      8.58
> 9    Placebo   WEEK 1      8.25
> ...
> 
> But I want to specify the variable (MyVar) as a character string:
> 
>    ddply(MyFrame, .(Treatment, Week), summarize,
> MeanValue=mean("MyVar"))
> 
> (Actually, the character string "MyVar" will be selected from a vector of
> character strings.)
> 
> The code above produces no joy:
> 
>    Treatment     Week MeanValue
> 1    MyDrug  BASELINE        NA
> 2    MyDrug    WEEK 1        NA
> 3    MyDrug    WEEK 2        NA
> 4    MyDrug    WEEK 3        NA
> ...
> I tried a few things, including:
> 
>   as.name("MyVar")
>   as.quoted("MyVar")
> 
> ... but they all produced the name results: NAs
> 
> I'm obviously thrashing around in the dark! Any advice would be greatly
> appreciated.
> 
> -John
> 
> 
> 	[[alternative HTML version deleted]]
> 
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