Re: [R] Question about a perceived irregularity in R syntax
On 23/07/2010 7:14 AM, Duncan Murdoch wrote: Nordlund, Dan (DSHS/RDA) wrote: >> -Original Message- >> From: r-help-boun...@r-project.org [mailto:r-help-boun...@r- >> project.org] On Behalf Of Peter Dalgaard >> Sent: Thursday, July 22, 2010 3:13 PM >> To: Pat Schmitz >> Cc: r-help@r-project.org >> Subject: Re: [R] Question about a perceived irregularity in R syntax >> >> Pat Schmitz wrote: >> >>> Both vector query's can select the values from the data.frame as >>> >> written, >> >>> however in the first form assigning a value to said selected numbers >>> >> fails. >> >>> Can you explain the reason this fails? >>> >>> dat <- data.frame(index = 1:10, Value = c(1:4, NA, 6, NA, 8:10)) >>> >>> dat$Value[dat$Value == "NA"] <- 1 #Why does this fails to work, >>> dat$Value[dat$Value %in% NA] <- 1 #While this does work? >>> >>> >>> #Particularly when str() results in an equivalent class >>> dat <- data.frame(index = 1:10, Value = c(1:4, NA, 6, NA, 8:10)) >>> str(dat$Value[dat$Value %in% NA]) >>> str(dat$Value[dat$Value == "NA"]) >>> >> 1. NA and "NA" are very different things >> 2. checkout is.na() and its help page >> >> >> > > I also would have suggested is.na to do the replacement. What surprised me was that > > dat$Value[dat$Value %in% NA] <- 1 > > actually worked. I guess I always assumed that if > > >> NA == NA >> > [1] NA > > then an attempt to compare NA to elements in a vector would also return NA, but not so. > > >> NA %in% c(1,NA,3) >> > [1] TRUE > > > Learned something new today, I suspect that's not intentional, though I'm not sure it should be fixed. According to the usual convention the result should be a logical NA. Oops, not true. The behaviour is clearly documented in ?match: Exactly what matches what is to some extent a matter of definition. For all types, ‘NA’ matches ‘NA’ and no other value. For real and complex values, ‘NaN’ values are regarded as matching any other ‘NaN’ value, but not matching ‘NA’. Thanks to Brian Ripley (the author of that paragraph) for pointing this out to me. Not sure how I missed it on my first reading, but the fact that it preceded my morning coffee might be a contributing factor. 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] Question about a perceived irregularity in R syntax
Nordlund, Dan (DSHS/RDA) wrote: -Original Message- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r- project.org] On Behalf Of Peter Dalgaard Sent: Thursday, July 22, 2010 3:13 PM To: Pat Schmitz Cc: r-help@r-project.org Subject: Re: [R] Question about a perceived irregularity in R syntax Pat Schmitz wrote: Both vector query's can select the values from the data.frame as written, however in the first form assigning a value to said selected numbers fails. Can you explain the reason this fails? dat <- data.frame(index = 1:10, Value = c(1:4, NA, 6, NA, 8:10)) dat$Value[dat$Value == "NA"] <- 1 #Why does this fails to work, dat$Value[dat$Value %in% NA] <- 1 #While this does work? #Particularly when str() results in an equivalent class dat <- data.frame(index = 1:10, Value = c(1:4, NA, 6, NA, 8:10)) str(dat$Value[dat$Value %in% NA]) str(dat$Value[dat$Value == "NA"]) 1. NA and "NA" are very different things 2. checkout is.na() and its help page I also would have suggested is.na to do the replacement. What surprised me was that dat$Value[dat$Value %in% NA] <- 1 actually worked. I guess I always assumed that if NA == NA [1] NA then an attempt to compare NA to elements in a vector would also return NA, but not so. NA %in% c(1,NA,3) [1] TRUE Learned something new today, I suspect that's not intentional, though I'm not sure it should be fixed. According to the usual convention the result should be a logical NA. 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] Question about a perceived irregularity in R syntax
> -Original Message- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r- > project.org] On Behalf Of Peter Dalgaard > Sent: Thursday, July 22, 2010 3:13 PM > To: Pat Schmitz > Cc: r-help@r-project.org > Subject: Re: [R] Question about a perceived irregularity in R syntax > > Pat Schmitz wrote: > > Both vector query's can select the values from the data.frame as > written, > > however in the first form assigning a value to said selected numbers > fails. > > Can you explain the reason this fails? > > > > dat <- data.frame(index = 1:10, Value = c(1:4, NA, 6, NA, 8:10)) > > > > dat$Value[dat$Value == "NA"] <- 1 #Why does this fails to work, > > dat$Value[dat$Value %in% NA] <- 1 #While this does work? > > > > > > #Particularly when str() results in an equivalent class > > dat <- data.frame(index = 1:10, Value = c(1:4, NA, 6, NA, 8:10)) > > str(dat$Value[dat$Value %in% NA]) > > str(dat$Value[dat$Value == "NA"]) > > 1. NA and "NA" are very different things > 2. checkout is.na() and its help page > > I also would have suggested is.na to do the replacement. What surprised me was that dat$Value[dat$Value %in% NA] <- 1 actually worked. I guess I always assumed that if > NA == NA [1] NA then an attempt to compare NA to elements in a vector would also return NA, but not so. > NA %in% c(1,NA,3) [1] TRUE Learned something new today, Dan Daniel J. Nordlund Washington State Department of Social and Health Services Planning, Performance, and Accountability Research and Data Analysis Division Olympia, WA 98504-5204 __ 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] Question about a perceived irregularity in R syntax
Pat Schmitz wrote: > Both vector query's can select the values from the data.frame as written, > however in the first form assigning a value to said selected numbers fails. > Can you explain the reason this fails? > > dat <- data.frame(index = 1:10, Value = c(1:4, NA, 6, NA, 8:10)) > > dat$Value[dat$Value == "NA"] <- 1 #Why does this fails to work, > dat$Value[dat$Value %in% NA] <- 1 #While this does work? > > > #Particularly when str() results in an equivalent class > dat <- data.frame(index = 1:10, Value = c(1:4, NA, 6, NA, 8:10)) > str(dat$Value[dat$Value %in% NA]) > str(dat$Value[dat$Value == "NA"]) 1. NA and "NA" are very different things 2. checkout is.na() and its help page -- Peter Dalgaard Center for Statistics, Copenhagen Business School 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.
