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% File src/library/base/man/ifelse.Rd
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% File src/library/base/man/ifelse.Rd
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% Part of the R package, https://www.R-project.org
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% Part of the R package, https://www.R-project.org
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% Copyright 1995-2015 R Core Team
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% Copyright 1995-2016 R Core Team
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% Distributed under GPL 2 or later
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% Distributed under GPL 2 or later
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\name{ifelse}
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\name{ifelse}
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\title{Conditional Element Selection}
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\title{Conditional Element Selection}
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\usage{
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\usage{
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## has many "yyyy-mm-29", but a few "yyyy-03-01" in the non-leap years
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## has many "yyyy-mm-29", but a few "yyyy-03-01" in the non-leap years
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y <- ifelse(as.POSIXlt(x)$mday == 29, x, NA)
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y <- ifelse(as.POSIXlt(x)$mday == 29, x, NA)
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head(y) # not what you expected ... ==> need restore the class attribute:
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head(y) # not what you expected ... ==> need restore the class attribute:
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class(y) <- class(x)
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class(y) <- class(x)
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y
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y
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## ==> Again a case where it is better *not* to use ifelse(), but
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## This is a (not atypical) case where it is better *not* to use ifelse(),
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## both more efficient and clear:
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## but rather the more efficient and still clear:
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y2 <- x
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y2 <- x
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y2[as.POSIXlt(x)$mday != 29] <- NA
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y2[as.POSIXlt(x)$mday != 29] <- NA
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## which gives the same as ifelse()+class() hack:
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stopifnot(identical(y2, y))
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stopifnot(identical(y2, y))
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## example of different return modes:
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## example of different return modes (and 'test' alone determining length):
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yes <- 1:3
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yes <- 1:3
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no <- pi^(0:3)
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no  <- pi^(1:4)
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typeof(ifelse(NA,    yes, no)) # logical
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utils::str( ifelse(NA,    yes, no) ) # logical, length 1
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typeof(ifelse(TRUE,  yes, no)) # integer
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utils::str( ifelse(TRUE,  yes, no) ) # integer, length 1
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typeof(ifelse(FALSE, yes, no)) # double
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utils::str( ifelse(FALSE, yes, no) ) # double,  length 1
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}
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}
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\keyword{logic}
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\keyword{logic}
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\keyword{programming}
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\keyword{programming}