[R] elements that appear only once
Hi. I have a factor and I want to extract just those elements that appear exactly once. How to do this? Toy example follows. a - as.factor(c(rep(oak,5) ,rep(ash,1),rep(elm,1),rep (beech,4))) a [1] oak oak oak oak oak ash elm beech beech beech beech Levels: ash beech elm oak table(a) a ash beech elm oak 1 4 1 5 So I would want ash and elm, because there is only one ash and only one elm in my wood. My Best Effort: names(table(a)[table(a)==1]) [1] ash elm This doesn't seem particularly elegant to me; there must be a better way! anyone? -- Robin Hankin Uncertainty Analyst National Oceanography Centre, Southampton European Way, Southampton SO14 3ZH, UK tel 023-8059-7743 __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] elements that appear only once
another approach is: names(which(table(a) == 1)) but I don't know if you find this more elegant :) Best, Dimitris Dimitris Rizopoulos Ph.D. Student Biostatistical Centre School of Public Health Catholic University of Leuven Address: Kapucijnenvoer 35, Leuven, Belgium Tel: +32/(0)16/336899 Fax: +32/(0)16/337015 Web: http://www.med.kuleuven.be/biostat/ http://www.student.kuleuven.be/~m0390867/dimitris.htm - Original Message - From: Robin Hankin [EMAIL PROTECTED] To: RHelp r-help@stat.math.ethz.ch Sent: Wednesday, February 22, 2006 10:11 AM Subject: [R] elements that appear only once Hi. I have a factor and I want to extract just those elements that appear exactly once. How to do this? Toy example follows. a - as.factor(c(rep(oak,5) ,rep(ash,1),rep(elm,1),rep (beech,4))) a [1] oak oak oak oak oak ash elm beech beech beech beech Levels: ash beech elm oak table(a) a ash beech elm oak 1 4 1 5 So I would want ash and elm, because there is only one ash and only one elm in my wood. My Best Effort: names(table(a)[table(a)==1]) [1] ash elm This doesn't seem particularly elegant to me; there must be a better way! anyone? -- Robin Hankin Uncertainty Analyst National Oceanography Centre, Southampton European Way, Southampton SO14 3ZH, UK tel 023-8059-7743 __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] elements that appear only once
Hi Dmitris, and list On 22 Feb 2006, at 09:24, Dimitris Rizopoulos wrote: another approach is: names(which(table(a) == 1)) but I don't know if you find this more elegant :) well, thank you for this (which() is good here!) but this is still inelegant IMHO because it uses the names() of a table. If I had a - as.factor(c(1,1,1,2,3,4,4,4,4,5)) names(which(table(a)==1)) [1] 2 3 5 this gives a character vector. I could coerce using as.integer() here, but this seems soinelegant. best wishes Robin Best, Dimitris Hi. I have a factor and I want to extract just those elements that appear exactly once. How to do this? Toy example follows. a - as.factor(c(rep(oak,5) ,rep(ash,1),rep(elm,1),rep (beech,4))) a [1] oak oak oak oak oak ash elm beech beech beech beech Levels: ash beech elm oak table(a) a ash beech elm oak 1 4 1 5 So I would want ash and elm, because there is only one ash and only one elm in my wood. My Best Effort: names(table(a)[table(a)==1]) [1] ash elm This doesn't seem particularly elegant to me; there must be a better way! anyone? -- Robin Hankin Uncertainty Analyst National Oceanography Centre, Southampton European Way, Southampton SO14 3ZH, UK tel 023-8059-7743 __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] elements that appear only once
A slight variation on your solution but hopefully more readable: names( which( table(a) == 1 ) ) Regards, Adai On Wed, 2006-02-22 at 09:11 +, Robin Hankin wrote: Hi. I have a factor and I want to extract just those elements that appear exactly once. How to do this? Toy example follows. a - as.factor(c(rep(oak,5) ,rep(ash,1),rep(elm,1),rep (beech,4))) a [1] oak oak oak oak oak ash elm beech beech beech beech Levels: ash beech elm oak table(a) a ash beech elm oak 1 4 1 5 So I would want ash and elm, because there is only one ash and only one elm in my wood. My Best Effort: names(table(a)[table(a)==1]) [1] ash elm This doesn't seem particularly elegant to me; there must be a better way! anyone? -- Robin Hankin Uncertainty Analyst National Oceanography Centre, Southampton European Way, Southampton SO14 3ZH, UK tel 023-8059-7743 __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] elements that appear only once
On Wed, 22 Feb 2006, Robin Hankin wrote: Hi Dmitris, and list On 22 Feb 2006, at 09:24, Dimitris Rizopoulos wrote: another approach is: names(which(table(a) == 1)) but I don't know if you find this more elegant :) Since the names of the table are the levels of the factor, I would use levels(a)[table(a) %in% 1] Well, almost. If you have NA or NaN as a factor level then all these solutions need to be more complicated. well, thank you for this (which() is good here!) but this is still inelegant IMHO because it uses the names() of a table. If I had a - as.factor(c(1,1,1,2,3,4,4,4,4,5)) names(which(table(a)==1)) [1] 2 3 5 this gives a character vector. I could coerce using as.integer() here, but this seems soinelegant. But a has a character vector of levels, and there is nothing there to tell R that you wanted integers and not decimal-digit character strings. -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UKFax: +44 1865 272595 __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] elements that appear only once
I am not sure whether this is desirable but here is another way just in case: paste(setdiff(a, a[duplicated(a)])) You could replace paste with as.character if you prefer or could remove it entirely if you want the result as a factor. On 2/22/06, Robin Hankin [EMAIL PROTECTED] wrote: Hi. I have a factor and I want to extract just those elements that appear exactly once. How to do this? Toy example follows. a - as.factor(c(rep(oak,5) ,rep(ash,1),rep(elm,1),rep (beech,4))) a [1] oak oak oak oak oak ash elm beech beech beech beech Levels: ash beech elm oak table(a) a ash beech elm oak 1 4 1 5 So I would want ash and elm, because there is only one ash and only one elm in my wood. My Best Effort: names(table(a)[table(a)==1]) [1] ash elm This doesn't seem particularly elegant to me; there must be a better way! anyone? -- Robin Hankin Uncertainty Analyst National Oceanography Centre, Southampton European Way, Southampton SO14 3ZH, UK tel 023-8059-7743 __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] elements that appear only once
Robin Hankin [EMAIL PROTECTED] writes: Hi Dmitris, and list On 22 Feb 2006, at 09:24, Dimitris Rizopoulos wrote: another approach is: names(which(table(a) == 1)) but I don't know if you find this more elegant :) well, thank you for this (which() is good here!) but this is still inelegant IMHO because it uses the names() of a table. If I had a - as.factor(c(1,1,1,2,3,4,4,4,4,5)) names(which(table(a)==1)) [1] 2 3 5 this gives a character vector. I could coerce using as.integer() here, but this seems soinelegant. You could go sort(unique(a))[table(a)==1] (without the sort(), things go pearshaped, try setting a - factor(c(1,1,1,2,3,4,4,4,4,5),levels=5:1) wnd you'll see). If we assume that a is a factor, another option is levels(a))[table(a)==1] but that also has the problem of returning a character vector. -- O__ Peter Dalgaard Øster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
