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As we know, it is possible to call functions in R without assigning them to the environment, e.g.
> (function(x){x/2})(5)
[1] 2.5
I would like to use functions like these, on the fly, in a mutate_each (or summarise_each) call. For example, with
df <- data.frame(a = runif(10), b = rnorm(10))
I might attempt to do one of the following, but they all return errors:
library(dplyr)
> df %>%
+ mutate_each(funs((function(x){x/2})), a, b)
Error in eval(substitute(expr), envir, enclos) :
Unsupported type CLOSXP for column "a"
>
> df %>%
+ mutate_each(list((function(x){x/2})), a, b)
Error: is.fun_list(calls) is not TRUE
>
>
> df %>%
+ mutate_each(funs((function(x){x/2})(.)), a, b)
Error in vapply(dots[missing_names], function(x) make_name(x$expr), character(1)) :
values must be length 1,
but FUN(X[[1]]) result is length 2
>
However, if I assign the function to the workspace, then all works as expected:
tmp_fn <- function(x){x/2}
and
> df %>%
+ mutate_each(funs(tmp_fn), a, b)
a b
1 0.360048105 -0.452285314
2 0.020175136 0.253063103
3 0.002351454 -0.148997643
4 0.262808493 -0.599555244
5 0.057246370 0.007567076
6 0.400027700 0.264901865
7 0.120505411 -0.346171709
8 0.266166200 0.116066231
9 0.031302148 -0.129739601
10 0.250212897 0.230194217
Is there a way to dynamically define functions in the call to mutate_each or summarise_each?
487
The () makes the anonymous function an expression that returns a function object. An anonymous function is not accessible after its initial creation. Therefore, you often need to assign it to a variable. In this example, the anonymous function has no name between the function keyword and parentheses () .
The advantage of an anonymous function is that it does not have to be stored in a separate file. This can greatly simplify programs, as often calculations are very simple and the use of anonymous functions reduces the number of code files necessary for a program.
An anonymous function is a function that was declared without any named identifier to refer to it. As such, an anonymous function is usually not accessible after its initial creation. Normal function definition: function hello() { alert('Hello world'); } hello();
They're called anonymous functions because they aren't given a name in the same way as normal functions. Because functions are first-class objects, we can pass a function as an argument in another function and later execute that passed-in function or even return it to be executed later.
We can wrap the function call with parentheses
df %>%
mutate_each(funs(((function(x){x/2})(.))))
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