Q:

R: fill down multiple columns

I'm using fill() from the tidyr package. fill(df, colname1, colname2, colname3) works fine, until I found a dataset with 32 variables. How should I fill down all columns without typing each name? 
I've tried:
fill(df,colnames(df)),
fill(df,1:32), 
fill(df,colname1:colname32). 

and produced the following errors:
Error: All select() inputs must resolve to integer column positions.
The following do not:
*  colnames(df1)

Error: tinyformat: Not enough conversion specifiers in format string

Error: tinyformat: Not enough conversion specifiers in format string

A:

We can use fill_ when we select variables with names. 
library(tidyr)# using tidyr_0.4.1.9000
res <- fill_(df, names(df))
head(res)
#   col1 col2 col3
#1    1   NA    b
#2    1    3    b
#3    2    4    a
#4    2    4    a
#5    2    1    a
#6    3    4    a

Other option would be 
fill(df, everything())

However, if we use fill with names(df)), it will give the same error as the OP showed
fill(df, names(df)[1])
#Error: All select() inputs must resolve to integer column positions.
#The following do not:
#*  names(df)[1]

data
set.seed(24)
 df <- data.frame(col1= sample(c(NA, 1:3), 20, replace=TRUE), 
                  col2 = sample(c(NA, 1:5), 20, replace=TRUE),
                  col3 = sample(c(NA, letters[1:5]), 20, replace=TRUE),
                  stringsAsFactors=FALSE)

