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adjusting "levels" after subset a table
3 messages · Milton Cezar Ribeiro, Marc Schwartz, Paulo Justiniano Ribeiro Jr
On Sat, 2007-12-08 at 19:26 -0800, Milton Cezar Ribeiro wrote:
Dear all, I have a data.frame with a factor collumn with about 10 levels. After extract a subset of this data.frame, by selecting 2 of my 10 levels, the new data.frame continue with original number of levels. How can I adjust it in a manner that when I try levels(my.df) I receive the actualyzed number of levels? By the way, I read my file using reab.table. I tryed solve it with : levels(my.df$my.var)<-unique(my.df$my.var) but the problem remain. Many thanks, miltinho Brazil
The default when subsetting factors (which happens when you subset a data frame) is to retain the original set of levels, even if they don't occur in the resultant subset. This is described in ?"[.factor" where the 'drop' argument is FALSE by default. To subset the factor and only retain levels for those values that are still present, you can use: MyFactor <- factor(MyFactor) or MyFactor <- MyFactor[, drop = TRUE] after subsetting the data frame. There is also a page in the R Wiki that describes some additional approaches: http://wiki.r-project.org/rwiki/doku.php?id=tips:data-manip:drop_unused_levels HTH, Marc Schwartz
running my.df$my.var <- factor(my.df$my.var) seems to do the job P.J.
On Sat, 8 Dec 2007, Milton Cezar Ribeiro wrote:
Dear all, I have a data.frame with a factor collumn with about 10 levels. After extract a subset of this data.frame, by selecting 2 of my 10 levels, the new data.frame continue with original number of levels. How can I adjust it in a manner that when I try levels(my.df) I receive the actualyzed number of levels? By the way, I read my file using reab.table. I tryed solve it with : levels(my.df$my.var)<-unique(my.df$my.var) but the problem remain. Many thanks, miltinho Brazil para armazenamento! [[alternative HTML version deleted]]
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Paulo Justiniano Ribeiro Jr LEG (Laboratorio de Estatistica e Geoinformacao) Universidade Federal do Parana Caixa Postal 19.081 CEP 81.531-990 Curitiba, PR - Brasil Tel: (+55) 41 3361 3573 Fax: (+55) 41 3361 3141 e-mail: paulojus AT ufpr br http://www.leg.ufpr.br/~paulojus ------------------------------------------------------------------------- 53a Reuniao Anual da Regiao Brasileira da Soc. Internacional de Biometria 14 a 16/05/2008, UFLA, Lavras,MG http://www.centenario.ufla.br/