Running Levene's test for each column of a df in R

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I have a data frame containing scores of several sub-scales of the same test (columns: participant, session, group, total score, one column per sub-scale). I am trying to run assumption checks for a two-way mixed ANOVA for each sub-scale. For convenience, I would like to write one loop per assumption check, that gives me the output for all sub-scales. This worked well for checking outliers, running Box's M test and for generating the actual ANOVA output. However, I get an error when trying the same thing with Levene's test. See code and errors below:

subscales <- c("awareness", "clarity", "impulse", "goals", "nonacceptance", 
               "strategies") # these correspond to the column names in the df
for (scale in subscales) {
  ders %>%
  group_by(session) %>%
  levene_test(scale ~ group) %>%
  kable(caption = scale) %>% print()
}

Error in mutate(., data = map(.data$data, .f, ...)) : Caused by error in model.frame.default(): ! variable lengths differ (found for 'group')

How can I run Levene's test for all columns in my df without just repeating the same code over and over? I'm new to R, so maybe I'm trying in a too pythonist kind of way and should use something like lapply() instead?

rstatix statistics r for-loop
1 Answers

Create the formula with reformulate as the scale will be quoted string and thus, it needs the formula to be constructed either with reformulate or paste

for (scale in subscales) {
  ders %>%
  group_by(session) %>%
  levene_test(reformulate('group', response = scale)) %>%
  kable(caption = scale) %>% print()
}

This maybe also done with across

library(dplyr)
library(stringr)
library(tidyr)
library(rstatix)
data(mtcars)
mtcars %>%
   mutate(carb = factor(carb)) %>%
   group_by(cyl) %>%
   summarise(across(c(mpg, disp), 
    ~ levene_test(cur_data(),
        reformulate('carb', response = cur_column())) %>% 
           rename_with(~ str_c(cur_column(), .x), everything()) )) %>% 
   unpack(where(is.tibble))

-output

# A tibble: 3 × 9
    cyl mpgdf1 mpgdf2 mpgstatistic  mpgp dispdf1 dispdf2 dispstatistic    dispp
  <dbl>  <int>  <int>        <dbl> <dbl>   <int>   <int>         <dbl>    <dbl>
1     4      1      9        0.975 0.349       1       9      1.32e- 1 7.24e- 1
2     6      2      4        2.52  0.196       2       4      7.44e+29 7.23e-60
3     8      3     10        1.60  0.251       3      10      1.18e+ 1 1.27e- 3
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