How to apply a shapiro test by groups in R?

Question

I have a dataframe where all my 90 variables have integer data, of the type:

code | variable1 | variable2 | variable3 | ...

AB | 2 | 3 | 10 |

Answer 1

Example with mtcars data.

library(tidyverse)
library(broom)

mtcars %>% 
    select(-am, - wt) %>% # Remove unnecessary columns
    gather(key = "variable_name", value = "value") %>%
    group_by(variable_name)  %>% 
    do(broom::tidy(shapiro.test(.$value)))  %>% 
    ungroup()  %>% 
    select(variable_name, W = statistic, `p-value` = p.value)

The result:

# A tibble: 9 x 3
  variable_name     W    `p-value`
                   
1 carb          0.851 0.000438    
2 cyl           0.753 0.00000606  
3 disp          0.920 0.0208      
4 drat          0.946 0.110       
5 gear          0.773 0.0000131   
6 hp            0.933 0.0488      
7 mpg           0.948 0.123       
8 qsec          0.973 0.594       
9 vs            0.632 0.0000000974