ifelse
Conditional Element Selection
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
.
 Keywords
 programming, logic
Usage
ifelse(test, yes, no)
Arguments
 test
 an object which can be coerced to logical mode.
 yes
 return values for true elements of
test
.  no
 return values for false elements of
test
.
Details
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.
Value

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
.
Warning
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
.
References
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
See Also
if
.
Examples
library(base)
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("20000229"), as.Date("20041004"), by = "1 month")
## has many "yyyymm29", but a few "yyyy0301" in the nonleap 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
Community examples
Example code for [LinkedIn Learning video](https://linkedinlearning.pxf.io/rweekly_ifelse) ```r # for example if (TRUE) { print("Leghorn") } else { print("Orpington") } ifelse(TRUE, "Leghorn", "Orpington") # or... if (TRUE) "Leghorn" else "Orpington" # if length(condition) > 1 ... MNRChickenRanch < c(1, 0, 0, 0, 1, 0, 0, 1, NA, 1, 1, 0, 1, 1, 0, 0, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 0) ifelse(MNRChickenRanch, "Leghorn", "Orpington") # The following fails because length(condition) == 1 if (MNRChickenRanch) "Leghorn" else "Orpington" # extra credit. I built the random # in MNR Chicken Ranch with this ifelse(runif(30) < .5, 0, 1) # or... sample(c(0,1),size = 30, replace = TRUE) # or... look up coin flip... ```
```r x < c(6:4) sqrt(x) # gives warning sqrt(ifelse(x >= 0, x, NA)) # no warning ```
```r x < c(6:4) sqrt(x) # gives warning sqrt(ifelse(x >= 0, x, NA)) # no warning ```