Consider this famous table (already exists in R)
head(iris)
Sepal.Length Sepal.Width Petal.Length Petal.Width Species
1 5.1 3.5 1.4 0.2 setosa
2 4.9 3.0 1.4 0.2 setosa
3 4.7 3.2 1.3 0.2 setosa
4 4.6 3.1 1.5 0.2 setosa
5 5.0 3.6 1.4 0.2 setosa
6 5.4 3.9 1.7 0.4 setosa
Please notice that it has a column named Sepal.Length. I defined a variable with the same name. Please consider this code:
table = iris
Sepal.Length = 0
table2 = table %>% mutate ( new = Sepal.Length*Petal.Length )
If you check the result:
head(table2)
Sepal.Length Sepal.Width Petal.Length Petal.Width Species new
1 5.1 3.5 1.4 0.2 setosa 0.28
2 4.9 3.0 1.4 0.2 setosa 0.28
3 4.7 3.2 1.3 0.2 setosa 0.26
4 4.6 3.1 1.5 0.2 setosa 0.30
5 5.0 3.6 1.4 0.2 setosa 0.28
6 5.4 3.9 1.7 0.4 setosa 0.68
As you see, the variable Sepal.Length = 0 has been ignored and the column table$Sepal.Length has been taken into account for creating the new column.
How can I have use variables in the calculations of mutate function?
Alternatively, put !! in front of Sepal.Length as noted here https://stackoverflow.com/a/47659705/13015865
packages
library(dplyr)
table <- iris #no need to change the name of the dataset. But ok.
Sepal.Length <- 0
table %>% mutate ( new = !!Sepal.Length*Petal.Length )
output (head)
Sepal.Length Sepal.Width Petal.Length Petal.Width Species new
1 5.1 3.5 1.4 0.2 setosa 0
2 4.9 3.0 1.4 0.2 setosa 0
3 4.7 3.2 1.3 0.2 setosa 0
4 4.6 3.1 1.5 0.2 setosa 0
5 5.0 3.6 1.4 0.2 setosa 0
6 5.4 3.9 1.7 0.4 setosa 0