# 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`

.

The `srcref`

attribute of functions is handled specially: if
`test`

is a simple true result and `yes`

evaluates to a function
with `srcref`

attribute, `ifelse`

returns `yes`

including
its attribute (the same applies to a false `test`

and `no`

argument). This functionality is only for backwards compatibility, the
form `if(test) yes else no`

should be used whenever `yes`

and
`no`

are functions.

##### 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)`

```
# NOT RUN {
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)$mday == 29, x, NA)
head(y) # not what you expected ... ==> need restore the class attribute:
class(y) <- class(x)
y
## This is a (not atypical) case where it is better *not* to use ifelse(),
## but rather the more efficient and still clear:
y2 <- x
y2[as.POSIXlt(x)$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
utils::str( ifelse(TRUE, yes, no) ) # integer, length 1
utils::str( ifelse(FALSE, yes, no) ) # double, length 1
# }
```

*Documentation reproduced from package base, version 3.5.1, License: Part of R 3.5.1*

### Community examples

**mark@niemannross.com**at Nov 24, 2018 base v3.5.1

Example code for [LinkedIn Learning video](https://linkedin-learning.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... ```

**duanzhichao2008@163.com**at Feb 15, 2017 base v3.3.2

```r x <- c(6:-4) sqrt(x) #- gives warning sqrt(ifelse(x >= 0, x, NA)) # no warning ```

**duanzhichao2008@163.com**at Feb 15, 2017 base v3.3.2

```r x <- c(6:-4) sqrt(x) #- gives warning sqrt(ifelse(x >= 0, x, NA)) # no warning ```