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.test."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.
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.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.
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)
## 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
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