[R] Help with ddply/summarize
David L Carlson
dcarlson at tamu.edu
Fri Nov 14 16:25:23 CET 2014
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
-------------------------------------
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
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