[R] standardize columns selectively within a dataframe
Dear all, I have a dataframe: df-dataframe(a=c(1,2,3),b=c(4,5,6),c=c(7,8,9),d=c(10,11,12)) I want to obtain a new dataframe with columns a and b being standardized ((x-mean(x))/sd(x)); the other two columns (c,d) I want to leave unchanged. What is the best way to achieve this? I have been trying to use subscripts but did not succeed so far. Any tips? Many thanks, Olga __ 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] standardize columns selectively within a dataframe
On Sep 1, 2010, at 10:35 AM, Olga Lyashevska wrote: Dear all, I have a dataframe: df-dataframe(a=c(1,2,3),b=c(4,5,6),c=c(7,8,9),d=c(10,11,12)) I want to obtain a new dataframe with columns a and b being standardized ((x-mean(x))/sd(x)); the other two columns (c,d) I want to leave unchanged. What is the best way to achieve this? I have been trying to use subscripts but did not succeed so far. df[ , 1:2] - scale(df[ , 1:2]) df a b c d 1 -1 -1 7 10 2 0 0 8 11 3 1 1 9 12 -- David Winsemius, MD West Hartford, CT __ 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] standardize columns selectively within a dataframe
If you want to scale within columns, you could try cbind( scale(df[,1:2]), df[ ,-c(1:2)] ) a b c d 1 -1 -1 7 10 2 0 0 8 11 3 1 1 9 12 and it is data.frame() btw. On 01/09/2010 15:35, Olga Lyashevska wrote: Dear all, I have a dataframe: df-dataframe(a=c(1,2,3),b=c(4,5,6),c=c(7,8,9),d=c(10,11,12)) I want to obtain a new dataframe with columns a and b being standardized ((x-mean(x))/sd(x)); the other two columns (c,d) I want to leave unchanged. What is the best way to achieve this? I have been trying to use subscripts but did not succeed so far. Any tips? Many thanks, Olga __ 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. __ 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] standardize columns selectively within a dataframe
Thanks! It is exactly what I was looking for! Cheers Olga __ 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] standardize columns selectively within a dataframe
On Sep 1, 2010, at 10:42 AM, David Winsemius wrote: On Sep 1, 2010, at 10:35 AM, Olga Lyashevska wrote: Dear all, I have a dataframe: df-dataframe(a=c(1,2,3),b=c(4,5,6),c=c(7,8,9),d=c(10,11,12)) I want to obtain a new dataframe with columns a and b being standardized ((x-mean(x))/sd(x)); the other two columns (c,d) I want to leave unchanged. What is the best way to achieve this? I have been trying to use subscripts but did not succeed so far. df[ , 1:2] - scale(df[ , 1:2]) df a b c d 1 -1 -1 7 10 2 0 0 8 11 3 1 1 9 12 I suspect you might have tried (df-mean(df))/sd(x) and gotten unsatisfactory results; I know I did. If you had really wanted to persist and do it from first principles, so to speak, or perhaps as homework, then consider the sweep operation. It takes an object of lower dimension and applies a function, (-) by default, with the third argument repeatedly across the specified (in the second argument) dimension. You wanted to work on columns, so this would accomplish the subtraction of means() followed by division by sd(): sweep(as.matrix(df[ , 1:2]), 2L, colMeans(mm)) # using the default - operator a b [1,] -1 -1 [2,] 0 0 [3,] 1 1 sweep(sweep(df[ , 1:2], 2L, colMeans(mm)), 2, sd(mm), /) a b 1 -1 -1 2 0 0 3 1 1 (Your test columns happened to be scaled already and only needed to be centered. This is how scale() does its work, and their help pages have links cross-referencing each other.) This is probably a good time to reference Burns', The R Inferno, which has an entry for sweep (p 57) as well tips regarding the drop=FALSE maneuver (p 54) that I tried first for this problem but it didn't work. -- David Winsemius, MD West Hartford, CT __ 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] standardize columns selectively within a dataframe
On Wed, 2010-09-01 at 12:42 -0400, David Winsemius wrote: I suspect you might have tried (df-mean(df))/sd(x) and gotten unsatisfactory results; I know I did. yes, indeed! a few times, but why is that? If you had really wanted to persist and do it from first principles, so to speak, or perhaps as homework, then consider the sweep operation. It takes an object of lower dimension and applies a function, (-) by default, with the third argument repeatedly across the specified (in the second argument) dimension. You wanted to work on columns, so this would accomplish the subtraction of means() followed by division by sd(): sweep(as.matrix(df[ , 1:2]), 2L, colMeans(mm)) # using the default - operator a b [1,] -1 -1 [2,] 0 0 [3,] 1 1 sweep(sweep(df[ , 1:2], 2L, colMeans(mm)), 2, sd(mm), /) a b 1 -1 -1 2 0 0 3 1 1 I am glad you are talking about sweep here, I have been also trying to use it, but never managed to get complete understanding of what it exactly does and therefore I could not get it working properly. Very clear explanation, thanks! (Your test columns happened to be scaled already and only needed to be centered. This is how scale() does its work, and their help pages have links cross-referencing each other.) This is probably a good time to reference Burns', The R Inferno, which has an entry for sweep (p 57) as well tips regarding the drop=FALSE maneuver (p 54) that I tried first for this problem but it didn't work. Thanks for the references! Your solution with scale() is nice and neat, but for the sake of learning it is useful to persist. Cheers, Olga __ 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.
