William Dunlap wrote:
-----Original Message-----
From: r-help-boun...@r-project.org
[mailto:r-help-boun...@r-project.org] On Behalf Of Erik Iverson
Sent: Wednesday, October 28, 2009 9:22 AM
To: Gurpal Kalsi; r-help@r-project.org
Subject: Re: [R] Selecting rows according to a column
Hello,
Here's an idea:
ifelse(z$c == "a", z$a, z$b)
If there may be many columns to select from (so
the nested ifelse's become tedious) one might try
> z[,-3][cbind(seq_len(nrow(z)),z$c)]
[1] 1 2 30 40 50
The initial [,-3] is there only so when the data.frame
is converted to a matrix by [.data.frame's processing
of a matrix subscript it becomes a numeric matrix, not
a character matrix.
Now _that's_ elegant!!
-Peter Ehlers
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
-----Original Message-----
From: r-help-boun...@r-project.org
[mailto:r-help-boun...@r-project.org]
On Behalf Of Gurpal Kalsi
Sent: Wednesday, October 28, 2009 11:15 AM
To: r-help@r-project.org
Subject: [R] Selecting rows according to a column
Hi,
With a data such as:
z = data.frame(a = 1:5, b=10*a, c = c("a", "a", "b", "b", "b") )
* a b c*
*1* 10 *a*
*2* 20 *a*
3 *30* *b*
4 *40* *b*
5 *50* *b*
Can anyone suggest a way to select [1, 2, 30, 40, 50],
ie. using column "c" to specify which column is selected
for each row.
Many thanks
G
[[alternative HTML version deleted]]
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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