[R] Use of parantheses to force order of execution
Hello, I wish to create a copy of a data frame, but with missing values replaced with NAs. I thought I should be able to do it in one step using parentheses to group the statements and force those inside the parens to execute first: df - (BWS6[BWS6 -998] - NA) But all this does is assign NA to df, as described in ?[ for the case with no parens. Can I do this in some way? It's no great problem of course to have two separate statements, just curious. Ben. [[alternative HTML version deleted]] __ 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] Use of parantheses to force order of execution
On 13-09-08 6:46 AM, Ben Harrison wrote: Hello, I wish to create a copy of a data frame, but with missing values replaced with NAs. I thought I should be able to do it in one step using parentheses to group the statements and force those inside the parens to execute first: df - (BWS6[BWS6 -998] - NA) But all this does is assign NA to df, as described in ?[ for the case with no parens. Can I do this in some way? It's no great problem of course to have two separate statements, just curious. This isn't an order of execution issue. Your parenthesized assignment modifies BWS6, and that's not what you want to do. If you convert BWS6 to a matrix instead of a dataframe, you could use res - ifelse(BWS6 -998, NA, BWS6) but ifelse doesn't work on dataframes in general. You can do it in one long line with a dataframe using lapply, but it is ugly: df - as.data.frame( lapply(BWS6, function(col) ifelse(col -998, NA, col))) Duncan Murdoch __ 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] Use of parantheses to force order of execution
On Sep 8, 2013, at 16:09 , Duncan Murdoch wrote: On 13-09-08 6:46 AM, Ben Harrison wrote: Hello, I wish to create a copy of a data frame, but with missing values replaced with NAs. I thought I should be able to do it in one step using parentheses to group the statements and force those inside the parens to execute first: df - (BWS6[BWS6 -998] - NA) But all this does is assign NA to df, as described in ?[ for the case with no parens. Can I do this in some way? It's no great problem of course to have two separate statements, just curious. This isn't an order of execution issue. Your parenthesized assignment modifies BWS6, and that's not what you want to do. Also, the value of an assignment is always the right hand side, in this case NA. The canonical way would be --- but There be Tygers There! --- this: df - `[-`(BWS6, BWS6 -998, NA) The Tygers are that R sometimes cheats in order to avoid duplication and assumes that `[-` can destructively modify its argument. So you shouldn't actually do the above. - Peter D. If you convert BWS6 to a matrix instead of a dataframe, you could use res - ifelse(BWS6 -998, NA, BWS6) but ifelse doesn't work on dataframes in general. You can do it in one long line with a dataframe using lapply, but it is ugly: df - as.data.frame( lapply(BWS6, function(col) ifelse(col -998, NA, col))) Duncan Murdoch __ 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. -- Peter Dalgaard, Professor, Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Email: pd@cbs.dk Priv: pda...@gmail.com __ 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] Use of parantheses to force order of execution
Thank you all for the replies. BWS6 is a data frame, but actually the main problem in my code as Duncan points out is that the statement inside the parentheses modifies BWS6 anyway. I need to rework my code. I coded my missing values for these data sets as -999.25 (a hangover from another piece of software that dumps out results). It's a rather dangerous thing to do, as in some cases I have discovered that when I write to csv, -999.25 is written as -999.2 or even -999 in some cases (haven't completely worked that out). Hence the awkward 998 expression. In respect of Duncan and Peter's solutions, I have found that R can be a troublesome pet at times, and this seems like one of them. Thanks for the help and warnings! Ben. On 9 September 2013 00:39, peter dalgaard pda...@gmail.com wrote: On Sep 8, 2013, at 16:09 , Duncan Murdoch wrote: On 13-09-08 6:46 AM, Ben Harrison wrote: Hello, I wish to create a copy of a data frame, but with missing values replaced with NAs. I thought I should be able to do it in one step using parentheses to group the statements and force those inside the parens to execute first: df - (BWS6[BWS6 -998] - NA) But all this does is assign NA to df, as described in ?[ for the case with no parens. Can I do this in some way? It's no great problem of course to have two separate statements, just curious. This isn't an order of execution issue. Your parenthesized assignment modifies BWS6, and that's not what you want to do. Also, the value of an assignment is always the right hand side, in this case NA. The canonical way would be --- but There be Tygers There! --- this: df - `[-`(BWS6, BWS6 -998, NA) The Tygers are that R sometimes cheats in order to avoid duplication and assumes that `[-` can destructively modify its argument. So you shouldn't actually do the above. - Peter D. If you convert BWS6 to a matrix instead of a dataframe, you could use res - ifelse(BWS6 -998, NA, BWS6) but ifelse doesn't work on dataframes in general. You can do it in one long line with a dataframe using lapply, but it is ugly: df - as.data.frame( lapply(BWS6, function(col) ifelse(col -998, NA, col))) Duncan Murdoch __ 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. -- Peter Dalgaard, Professor, Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Email: pd@cbs.dk Priv: pda...@gmail.com [[alternative HTML version deleted]] __ 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.
