Why ifelse with character statement is not working? - r

Question

I am having problem today to understand how functions works.
This is my code:
my_fun<- function(x){
ifelse(as.character(x) == 'Species',
a<- iris %>% select(x),
a<- iris*2)
a
}
my_fun(x = Species)
Why is it not working?

Answer 1

There are three changes to be made,
converting to character would be with deparse/substitute
if/else would be appropriate as ifelse requires all the arguments to be of same length
iris * 2 as an else option wouldn't work as the dataset includes a factor column as well. So, we need to multiply only those numeric columns
my_fun <- function(x) {
x <- deparse(substitute(x))
if(x == 'Species') {
iris %>%
select(all_of(x))
} else {
iris %>%
mutate(across(where(is.numeric), ~ .* 2))
}
}
-testing
my_fun(Species)
# Species
#1 setosa
#2 setosa
#3 setosa
#4 setosa
#5 setosa
#6 setosa
#...
and if we pass another input
my_fun(hello)
# Sepal.Length Sepal.Width Petal.Length Petal.Width Species
#1 10.2 7.0 2.8 0.4 setosa
#2 9.8 6.0 2.8 0.4 setosa
#3 9.4 6.4 2.6 0.4 setosa
#4 9.2 6.2 3.0 0.4 setosa
#5 10.0 7.2 2.8 0.4 setosa
#6 10.8 7.8 3.4 0.8 setosa
# ...

Answer 2

library(tidyverse)
my_fun <- function(x) {
if(x == "Species") {
iris %>% select(x)
} else {
iris * 2
}
}
my_fun("Species")
Why?
You have an error because Species when evaluated is not found since it was not a defined variable.
One can use Non Standard Evaluation (NSE) feature with deparse and substitute see #akrun answer. But maybe you want to call your function with a character like that my_fun("Species").
The other mistake is that ifelse is a vectorized version of if/else and here you just want to test one value (x).

Answer 3

If you would like to ifelse anyway, here is a variation base on answers by #akrun and #pietrodito
my_fun <- function(x) {
x <- deparse(substitute(x))
ifelse(x == "Species",
a <- list(iris %>% select(x)),
a <- list(iris * 2)
)
a[[1]]
}
which gives
> my_fun(Species)
Species
1 setosa
2 setosa
3 setosa
4 setosa
5 setosa
6 setosa
7 setosa
8 setosa
9 setosa
10 setosa
11 setosa
12 setosa
13 setosa
14 setosa
15 setosa
16 setosa
17 setosa
18 setosa
19 setosa
20 setosa
21 setosa
22 setosa
23 setosa
24 setosa
25 setosa
26 setosa
27 setosa
28 setosa
29 setosa
30 setosa
31 setosa
32 setosa
33 setosa
34 setosa
35 setosa
36 setosa
37 setosa
38 setosa
39 setosa
40 setosa
41 setosa
42 setosa
43 setosa
44 setosa
45 setosa
46 setosa
47 setosa
48 setosa
49 setosa
50 setosa
51 versicolor
52 versicolor
53 versicolor
54 versicolor
55 versicolor
56 versicolor
57 versicolor
58 versicolor
59 versicolor
60 versicolor
61 versicolor
62 versicolor
63 versicolor
64 versicolor
65 versicolor
66 versicolor
67 versicolor
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88 versicolor
89 versicolor
90 versicolor
91 versicolor
92 versicolor
93 versicolor
94 versicolor
95 versicolor
96 versicolor
97 versicolor
98 versicolor
99 versicolor
100 versicolor
101 virginica
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