How to call a function in a loop to compute weighted crosstables in R

Question

I want to compute several weighted crosstables between the variable x and several y variables of the same dataframe. I created a function to do that, but I can´t loop my list of y variables.

I am giving an example of my procedure using mpg data: here, my y variables are cyl and year. x is class.

library(questionr)

# include some weights in mpg2 (same weight)

mpg2 <- mpg %>%
  mutate(weight = 1/234)
#> Error in mpg %>% mutate(weight = 1/234): could not find function "%>%"

# crosstab class by cyl using weights
questionr::wtd.table(mpg2$class, mpg2$cyl,
                                  weights=mpg2$weight,
                                  digits = 0, na.show=FALSE)
#> Error in questionr::wtd.table(mpg2$class, mpg2$cyl, weights = mpg2$weight, : object 'mpg2' not found

# using a function
calc_table <- function(x, y) {
  return(questionr::wtd.table(x, y,
                       weights=mpg2$weight,
                       digits = 0, na.show=FALSE))
}

# No problem when describing the variable as mpg2$cyl
calc_table(mpg2$class, mpg2$cyl)
#> Error in questionr::wtd.table(x, y, weights = mpg2$weight, digits = 0, : object 'mpg2' not found

# But I want to crosstab class with cyl (mpg2[5])
# and also class with year (mpg2[4]) 
# referencing the variable in a loop
# My main goal is to use the function for several variables

for (i in c(4:5)){
  calc_table(mpg2$class, mpg2[i])
}
#> Error in questionr::wtd.table(x, y, weights = mpg2$weight, digits = 0, : object 'mpg2' not found

Answer 1

The issue is that you used mpg2[i] which returns a dataframe or tibble instead of mpg2[[i]] which returns a vector. However, besides this issue I would suggest to loop over column names instead of positions. I also added a list to save the results. Try this:

library(dplyr)
library(questionr)

# include some weights in mpg2 (same weight)

mpg2 <- ggplot2::mpg %>%
  mutate(weight = 1/234)

# using a function
calc_table <- function(x, y) {
  questionr::wtd.table(x, y, weights=mpg2$weight, digits = 0, na.show=FALSE)
}

table_list <- list()
for (i in c("cyl", "year")){
  print(table_list[[i]] <- calc_table(mpg2$class, mpg2[[i]]))
}
#>                      4           5           6           8
#> 2seater    0.000000000 0.000000000 0.000000000 0.021367521
#> compact    0.136752137 0.008547009 0.055555556 0.000000000
#> midsize    0.068376068 0.000000000 0.098290598 0.008547009
#> minivan    0.004273504 0.000000000 0.042735043 0.000000000
#> pickup     0.012820513 0.000000000 0.042735043 0.085470085
#> subcompact 0.089743590 0.008547009 0.029914530 0.021367521
#> suv        0.034188034 0.000000000 0.068376068 0.162393162
#>                   1999        2008
#> 2seater    0.008547009 0.012820513
#> compact    0.106837607 0.094017094
#> midsize    0.085470085 0.089743590
#> minivan    0.025641026 0.021367521
#> pickup     0.068376068 0.072649573
#> subcompact 0.081196581 0.068376068
#> suv        0.123931624 0.141025641