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What is the practical use of the identity function in R?

Asked 2011-08-18T14:14:54.127
40

Base R defines an identity function, a trivial identity function returning its argument (quoting from ?identity).

It is defined as :

identity <- function (x){x}

Why would such a trivial function ever be useful? Why would it be included in base R?

r functional-programming identity
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13

I use it from time to time with the apply function of commands.

For instance, you could write t() as:

dat <- data.frame(x=runif(10),y=runif(10))
apply(dat,1,identity)

       [,1]      [,2]      [,3]      [,4]      [,5]      [,6]       [,7]
x 0.1048485 0.7213284 0.9033974 0.4699182 0.4416660 0.1052732 0.06000952
y 0.7225307 0.2683224 0.7292261 0.5131646 0.4514837 0.3788556 0.46668331
       [,8]      [,9]      [,10]
x 0.2457748 0.3833299 0.86113771
y 0.9643703 0.3890342 0.01700427
answered 2011-08-18T14:32:56.593

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