R: Examples for 'base::ifelse'

### ** Examples

x <- c(6:-4)
sqrt(x)  #- gives warning

Warning in sqrt(x): NaNs produced

 [1] 2.449490 2.236068 2.000000 1.732051 1.414214 1.000000 0.000000      NaN
 [9]      NaN      NaN      NaN

sqrt(ifelse(x >= 0, x, NA))  # no warning

 [1] 2.449490 2.236068 2.000000 1.732051 1.414214 1.000000 0.000000       NA
 [9]       NA       NA       NA

## Note: the following also gives the warning !
ifelse(x >= 0, sqrt(x), NA)

Warning in sqrt(x): NaNs produced

 [1] 2.449490 2.236068 2.000000 1.732051 1.414214 1.000000 0.000000       NA
 [9]       NA       NA       NA

## ifelse() strips attributes
## This is important when working with Dates and factors
x <- seq(as.Date("2000-02-29"), as.Date("2004-10-04"), by = "1 month")
## has many "yyyy-mm-29", but a few "yyyy-03-01" in the non-leap years
y <- ifelse(as.POSIXlt(x)$mday == 29, x, NA)
head(y) # not what you expected ... ==> need restore the class attribute:

[1] 11016 11045 11076 11106 11137 11167

class(y) <- class(x)
y

 [1] "2000-02-29" "2000-03-29" "2000-04-29" "2000-05-29" "2000-06-29"
 [6] "2000-07-29" "2000-08-29" "2000-09-29" "2000-10-29" "2000-11-29"
[11] "2000-12-29" "2001-01-29" NA           "2001-03-29" "2001-04-29"
[16] "2001-05-29" "2001-06-29" "2001-07-29" "2001-08-29" "2001-09-29"
[21] "2001-10-29" "2001-11-29" "2001-12-29" "2002-01-29" NA          
[26] "2002-03-29" "2002-04-29" "2002-05-29" "2002-06-29" "2002-07-29"
[31] "2002-08-29" "2002-09-29" "2002-10-29" "2002-11-29" "2002-12-29"
[36] "2003-01-29" NA           "2003-03-29" "2003-04-29" "2003-05-29"
[41] "2003-06-29" "2003-07-29" "2003-08-29" "2003-09-29" "2003-10-29"
[46] "2003-11-29" "2003-12-29" "2004-01-29" "2004-02-29" "2004-03-29"
[51] "2004-04-29" "2004-05-29" "2004-06-29" "2004-07-29" "2004-08-29"
[56] "2004-09-29"

## This is a (not atypical) case where it is better *not* to use ifelse(),
## but rather the more efficient and still clear:
y2 <- x
y2[as.POSIXlt(x)$mday != 29] <- NA
## which gives the same as ifelse()+class() hack:
stopifnot(identical(y2, y))


## example of different return modes (and 'test' alone determining length):
yes <- 1:3
no  <- pi^(1:4)
utils::str( ifelse(NA,    yes, no) ) # logical, length 1

 logi NA

utils::str( ifelse(TRUE,  yes, no) ) # integer, length 1

 int 1

utils::str( ifelse(FALSE, yes, no) ) # double,  length 1

 num 3.14

Examples for 'base::ifelse'

Conditional Element Selection