ifelse

0th

Percentile

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.

Aliases
  • ifelse
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 ```