Your code suggests that you do not understand R or what you are doing. The line
mydata$newvar[oldvar = "topic1"] <- "parenttopic"
does not recode cases where oldvar is "topic1", it creates a new variable
called oldvar (not the same as mydata$oldvar) and sets it to "topic1" because a
single equals sign assigns a value to a variable whereas two equals signs
create a logical expression. The result is that all values of mydata$newvar
become "parenttopic". You did not give us any data, so it is not clear if
oldvar is a character variable or a factor. Assuming it is a factor try the
following and then spend a few hours reading some tutorials on R:
> # Create reproducible data
> set.seed(42)
> mydata <- data.frame(oldvar=paste("topic", sample(1:20, 200, replace=TRUE)))
> str(mydata)
'data.frame': 200 obs. of 1 variable:
$ oldvar: Factor w/ 20 levels "topic 1","topic 10",..: 11 11 17 9 5 3 7 14 6 7
...
> # Note factor levels are ordered alphabetically. Fix that with
> mydata$oldvar <- factor(mydata$oldvar, levels=c(paste("topic", 1:20)))
> str(mydata)
'data.frame': 200 obs. of 1 variable:
$ oldvar: Factor w/ 20 levels "topic 1","topic 2",..: 19 19 6 17 13 11 15 3 14
15 ...
> levels(mydata$oldvar)
[1] "topic 1" "topic 2" "topic 3" "topic 4" "topic 5" "topic 6" "topic
7" "topic 8"
[9] "topic 9" "topic 10" "topic 11" "topic 12" "topic 13" "topic 14" "topic
15" "topic 16"
[17] "topic 17" "topic 18" "topic 19" "topic 20"
> mydata$newvar <- mydata$oldvar
> levels(mydata$newvar)[c(1, 9, 14)] <- "parenttopic"
> table(mydata$newvar)
parenttopic topic 2 topic 3 topic 4 topic 5 topic 6
topic 7 topic 8
26 6 14 10 8 7
7 11
topic 10 topic 11 topic 12 topic 13 topic 15 topic 16
topic 17 topic 18
8 10 9 13 19 12
11 3
topic 19 topic 20
18 8
-------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77840-4352
-----Original Message-----
From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of MACDOUGALL
Margaret
Sent: Monday, October 10, 2016 9:56 AM
To: r-help@r-project.org
Subject: [R] Recoding lists of categories of a variable
Hello
The R code
mydata$newvar[oldvar = "topic1"] <- "parenttopic"
is intended to recode the category 'topic 1' of the old varaible 'oldvar' a
new category label 'parenttopic' by defining the new variable 'newvar'.
Is there a convenient way to edit this code to allow me to recode a list of
categories 'topic 1', 'topic 9' and 'topic 14', say, of the the old variable
'oldvar' as 'parenttopic' by means of the new variable 'newvar', while also
mapping system missing values to system missing values?
Thanks in advance
Best wishes
Margaret
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