[R] drop unused levels in subset.data.frame
Dear list,
subset has a 'drop' argument that I had often mistaken for the one in
[.factor which removes unused levels.
Clearly it doesn't work that way, as shown below,
d - data.frame(x = factor(letters[1:15]), y = factor(LETTERS[1:3]))
s - subset(d, y==A, drop=TRUE)
str(s)
'data.frame': 5 obs. of 2 variables:
$ x: Factor w/ 15 levels a,b,c,d,..: 1 4 7 10 13
$ y: Factor w/ 3 levels A,B,C: 1 1 1 1 1
The subset still retains all the unused factor levels. I wonder how
people usually get rid of all unused levels in a data.frame after
subsetting? I came up with this but I may have missed a better
built-in solution,
dropit - function (d, columns = names(d), ...)
{
d[columns] = lapply(d[columns], [, drop=TRUE, ...)
d
}
str(dropit(s))
'data.frame': 5 obs. of 2 variables:
$ x: Factor w/ 5 levels a,d,g,j,..: 1 2 3 4 5
$ y: Factor w/ 1 level A: 1 1 1 1 1
Best regards,
baptiste
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Re: [R] drop unused levels in subset.data.frame
On Nov 10, 2009, at 10:49 AM, baptiste auguie wrote:
Dear list,
subset has a 'drop' argument that I had often mistaken for the one in
[.factor which removes unused levels.
Clearly it doesn't work that way, as shown below,
d - data.frame(x = factor(letters[1:15]), y = factor(LETTERS[1:3]))
s - subset(d, y==A, drop=TRUE)
str(s)
'data.frame': 5 obs. of 2 variables:
$ x: Factor w/ 15 levels a,b,c,d,..: 1 4 7 10 13
$ y: Factor w/ 3 levels A,B,C: 1 1 1 1 1
The subset still retains all the unused factor levels. I wonder how
people usually get rid of all unused levels in a data.frame after
subsetting? I came up with this but I may have missed a better
built-in solution,
dropit - function (d, columns = names(d), ...)
{
d[columns] = lapply(d[columns], [, drop=TRUE, ...)
d
}
If you are looking for a one-liner, then consider:
data.frame(lapply(s, function(x) if (is.factor(x)){ factor(x)} else
{x}))
I added a numeric column to make sure I had not clobbered a non-factor
variable.
d - data.frame(x = factor(letters[1:15]), y =
factor(LETTERS[1:3]), N=1:15)
s - subset(d, y==A, drop=TRUE)
str( data.frame(lapply(s, function(x) if (is.factor(x)){ factor(x)}
else {x})) )
'data.frame': 5 obs. of 3 variables:
$ x: Factor w/ 5 levels a,d,g,j,..: 1 2 3 4 5
$ y: Factor w/ 1 level A: 1 1 1 1 1
$ N: int 1 4 7 10 13
str(dropit(s))
'data.frame': 5 obs. of 2 variables:
$ x: Factor w/ 5 levels a,d,g,j,..: 1 2 3 4 5
$ y: Factor w/ 1 level A: 1 1 1 1 1
Best regards,
baptiste
__
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https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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Re: [R] drop unused levels in subset.data.frame
On Nov 10, 2009, at 9:49 AM, baptiste auguie wrote:
Dear list,
subset has a 'drop' argument that I had often mistaken for the one in
[.factor which removes unused levels.
Clearly it doesn't work that way, as shown below,
d - data.frame(x = factor(letters[1:15]), y = factor(LETTERS[1:3]))
s - subset(d, y==A, drop=TRUE)
str(s)
'data.frame': 5 obs. of 2 variables:
$ x: Factor w/ 15 levels a,b,c,d,..: 1 4 7 10 13
$ y: Factor w/ 3 levels A,B,C: 1 1 1 1 1
The subset still retains all the unused factor levels. I wonder how
people usually get rid of all unused levels in a data.frame after
subsetting? I came up with this but I may have missed a better
built-in solution,
dropit - function (d, columns = names(d), ...)
{
d[columns] = lapply(d[columns], [, drop=TRUE, ...)
d
}
str(dropit(s))
'data.frame': 5 obs. of 2 variables:
$ x: Factor w/ 5 levels a,d,g,j,..: 1 2 3 4 5
$ y: Factor w/ 1 level A: 1 1 1 1 1
There is a page in the R wiki here:
http://wiki.r-project.org/rwiki/doku.php?id=tips:data-manip:drop_unused_levels
that has some approaches.
HTH,
Marc Schwartz
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Re: [R] drop unused levels in subset.data.frame
Neat, I reinvented the wheel! Would that seem like a useful example at
the end of the help page for ?subset ? (it currently has very little
to say about drop).
Thanks also to David for the alternative idea.
Best regards,
baptiste
2009/11/10 Marc Schwartz marc_schwa...@me.com:
On Nov 10, 2009, at 9:49 AM, baptiste auguie wrote:
Dear list,
subset has a 'drop' argument that I had often mistaken for the one in
[.factor which removes unused levels.
Clearly it doesn't work that way, as shown below,
d - data.frame(x = factor(letters[1:15]), y = factor(LETTERS[1:3]))
s - subset(d, y==A, drop=TRUE)
str(s)
'data.frame': 5 obs. of 2 variables:
$ x: Factor w/ 15 levels a,b,c,d,..: 1 4 7 10 13
$ y: Factor w/ 3 levels A,B,C: 1 1 1 1 1
The subset still retains all the unused factor levels. I wonder how
people usually get rid of all unused levels in a data.frame after
subsetting? I came up with this but I may have missed a better
built-in solution,
dropit - function (d, columns = names(d), ...)
{
d[columns] = lapply(d[columns], [, drop=TRUE, ...)
d
}
str(dropit(s))
'data.frame': 5 obs. of 2 variables:
$ x: Factor w/ 5 levels a,d,g,j,..: 1 2 3 4 5
$ y: Factor w/ 1 level A: 1 1 1 1 1
There is a page in the R wiki here:
http://wiki.r-project.org/rwiki/doku.php?id=tips:data-manip:drop_unused_levels
that has some approaches.
HTH,
Marc Schwartz
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] drop unused levels in subset.data.frame
If you don't want to preserve factor levels when subsetting use
characters. There are very few other differences in behavior.
Hadley
On Tuesday, November 10, 2009, baptiste auguie
baptiste.aug...@googlemail.com wrote:
Dear list,
subset has a 'drop' argument that I had often mistaken for the one in
[.factor which removes unused levels.
Clearly it doesn't work that way, as shown below,
d - data.frame(x = factor(letters[1:15]), y = factor(LETTERS[1:3]))
s - subset(d, y==A, drop=TRUE)
str(s)
'data.frame': 5 obs. of 2 variables:
$ x: Factor w/ 15 levels a,b,c,d,..: 1 4 7 10 13
$ y: Factor w/ 3 levels A,B,C: 1 1 1 1 1
The subset still retains all the unused factor levels. I wonder how
people usually get rid of all unused levels in a data.frame after
subsetting? I came up with this but I may have missed a better
built-in solution,
dropit - function (d, columns = names(d), ...)
{
d[columns] = lapply(d[columns], [, drop=TRUE, ...)
d
}
str(dropit(s))
'data.frame': 5 obs. of 2 variables:
$ x: Factor w/ 5 levels a,d,g,j,..: 1 2 3 4 5
$ y: Factor w/ 1 level A: 1 1 1 1 1
Best regards,
baptiste
__
r-h...@r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
--
http://had.co.nz/
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