Hi!
25.08.2015, 18:17, Sam Albers wrote:
Hi all,
This is a process question. How do folks efficiently identify column
numbers in a dataframe without manually counting them. For example, if I
want to choose columns from the iris dataframe I know of two options. I can
do this:
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 ...
or this:
names(iris)[1] "Sepal.Length" "Sepal.Width" "Petal.Length" "Petal.Width"
"Species"
Neither option explicitly identifies the column number so that I can
do something like this:
iris[,c(2,4)]
I feel like there must be a better way to do this so I wanted to ask
the collective wisdom here what people do to accomplish this.
Obviously this is a trivial example, but the issue really becomes
problematic when you have a large dataframe.
Maybe with 'which'?
> which(colnames(iris)=="Sepal.Length")
[1] 1
Or did I somehow misunderstood what you are looking for?
HTH,
Kimmo
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