on 07/02/2008 02:10 PM R_Learner wrote:
raw <- read.csv(file=filename, head=TRUE,sep=",")
I've read in a csv file, and I'm looking to access a column whose name is
held in a string.
For example, I want to access raw$one or raw$two, but this will depending on
the string. Let's say that the string is decision<-"one". How would I access
raw$one?
The following doesn't work:
numbers<-raw$decision
Please help me!
Thanks!
> str(iris)
'data.frame': 150 obs. of 5 variables:
$ Sepal.Length: num 5.1 4.9 4.7 4.6 5 5.4 4.6 5 4.4 4.9 ...
$ Sepal.Width : num 3.5 3 3.2 3.1 3.6 3.9 3.4 3.4 2.9 3.1 ...
$ Petal.Length: num 1.4 1.4 1.3 1.5 1.4 1.7 1.4 1.5 1.4 1.5 ...
$ Petal.Width : num 0.2 0.2 0.2 0.2 0.2 0.4 0.3 0.2 0.2 0.1 ...
$ Species : Factor w/ 3 levels "setosa","versicolor",..: 1 1 1 1 1
1 1 1 1 1 ...
MyCol <- "Petal.Length"
# Use column indexing
> iris[, MyCol]
[1] 1.4 1.4 1.3 1.5 1.4 1.7 1.4 1.5 1.4 1.5 1.5 1.6 1.4 1.1 1.2 1.5
[17] 1.3 1.4 1.7 1.5 1.7 1.5 1.0 1.7 1.9 1.6 1.6 1.5 1.4 1.6 1.6 1.5
...
# Use list indexing. A data frame is a list...
> iris[[MyCol]]
[1] 1.4 1.4 1.3 1.5 1.4 1.7 1.4 1.5 1.4 1.5 1.5 1.6 1.4 1.1 1.2 1.5
[17] 1.3 1.4 1.7 1.5 1.7 1.5 1.0 1.7 1.9 1.6 1.6 1.5 1.4 1.6 1.6 1.5
# Use subset()
> subset(iris, select = MyCol)
Petal.Length
1 1.4
2 1.4
3 1.3
4 1.5
5 1.4
...
See ?"[.data.frame" and ?subset
HTH,
Marc Schwartz
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