Passing a column name to R tidyr spread

Question

I am trying to pass an object with the column name to the spread function, but instead of reading the value inside the object it just tries to use the object name itself

Here just a toy example

library(tidyr)
d = (1:4)
n = c("a"," a", "b","b") 
s = c(1, 2,5,7) 

df = data.frame(d,n, s) 

Value <- n
data_wide <- spread(df, Value , s)

Error: Key column 'Value' does not exist in input.

whilst below works fine:

data_wide <- spread(df, n, s)
d  a  a  b
1 1 NA  1 NA
2 2  2 NA NA
3 3 NA NA  5
4 4 NA NA  7

Answer 1

We can use spread_() to pass variable names as strings:

library(tidyr)
# dummy data
df1 <- data.frame(d = (1:4),
                  n = c("a", "a", "b", "b") ,
                  s = c(1, 2, 5, 7)) 

myKey <- "n"
myValue <- "s"
spread_(data = df1, key_col = myKey , value_col = myValue)

Answer 2

Using data.table

library(data.table)
 dcast(setDT(df), eval(as.name(myValue))~ eval(as.name(myKey)), value.var=myValue)

Regarding passing names in tidyr functions, this answer could also help (which was posted a couple of hours back).