ifelse {base} | R Documentation |
ifelse
returns a value with the same shape as
test
which is filled with elements selected
from either yes
or no
depending on whether the element of test
is TRUE
or FALSE
.
ifelse(test, yes, no)
test |
an object which can be coerced to logical mode. |
yes |
return values for true elements of |
no |
return values for false elements of |
If yes
or no
are too short, their elements are recycled.
yes
will be evaluated if and only if any element of test
is true, and analogously for no
.
Missing values in test
give missing values in the result.
A vector of the same length and attributes (including dimensions and
"class"
) as test
and data values from the values of
yes
or no
. The mode of the answer will be coerced from
logical to accommodate first any values taken from yes
and then
any values taken from no
.
The mode of the result may depend on the value of test
(see the
examples), and the class attribute (see oldClass
) of the
result is taken from test
and may be inappropriate for the
values selected from yes
and no
.
Sometimes it is better to use a construction such as
(tmp <- yes; tmp[!test] <- no[!test]; tmp)
, possibly extended to handle missing values in test
.
Further note that if(test) yes else no
is much more efficient
and often much preferable to ifelse(test, yes, no)
whenever
test
is a simple true/false result, i.e., when
length(test) == 1
.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
if
.
x <- c(6:-4) sqrt(x) #- gives warning sqrt(ifelse(x >= 0, x, NA)) # no warning ## Note: the following also gives the warning ! ifelse(x >= 0, sqrt(x), 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)$mday == 29, x, NA) head(y) # not what you expected ... ==> need restore the class attribute: class(y) <- class(x) y ## ==> Again a case where it is better *not* to use ifelse(), but ## both more efficient and clear: y2 <- x y2[as.POSIXlt(x)$mday != 29] <- NA stopifnot(identical(y2, y)) ## example of different return modes: yes <- 1:3 no <- pi^(0:3) typeof(ifelse(NA, yes, no)) # logical typeof(ifelse(TRUE, yes, no)) # integer typeof(ifelse(FALSE, yes, no)) # double