How do I reiterate through multiple variables - r

Question

I have a sample dataset as below:
Day<-c(1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2,2,2)
Group<-c("A","A","A","B","B","B","C","C","C","A","A","A","A","B","B","B","C","C","C")
Rain<-c(4,4,6,5,3,4,5,5,3,6,6,6,5,3,3,3,2,5,2)
UV<-c(6,6,7,8,5,6,5,6,6,6,7,7,8,8,5,6,8,5,7)
dat<-data.frame(Day,Group,Rain,UV)
I want to run a Kruskal Wallis test among 'A','B' and 'C' in "Group" for the variables "Rain" and "UV".
At present, I am subsetting the variables one by one for Kruskal test as below:
dat_Rain<-dat%>%select(c(Day,Group,Rain))
library(rstatix)
library(tidyverse)
dat_Rain%>%
group_by(Day) %>%
kruskal_test(Rain ~ Group)
How do I reiterate Kruskal test for multiple variables (Rain,UV) in this dataset? Thanks.

Answer 1

You can define the columns that you want to apply kruskal_test and use map_df to get all the values in one dataframe.
library(rstatix)
library(tidyverse)
cols <- c('Rain', 'UV')
map_df(cols, ~dat %>% group_by(Day) %>% kruskal_test(reformulate('Group', .x)))
# Day .y. n statistic df p method
# <dbl> <chr> <int> <dbl> <int> <dbl> <chr>
#1 1 Rain 9 0.505 2 0.777 Kruskal-Wallis
#2 2 Rain 10 6.52 2 0.0384 Kruskal-Wallis
#3 1 UV 9 1.16 2 0.56 Kruskal-Wallis
#4 2 UV 10 0.423 2 0.809 Kruskal-Wallis

Answer 2

Using lapply and making use of a helper function this could be achieved like so:
Additionally I made use of bind_rows to bind the resulting list into one data frame.
Day<-c(1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2,2,2)
Group<-c("A","A","A","B","B","B","C","C","C","A","A","A","A","B","B","B","C","C","C")
Rain<-c(4,4,6,5,3,4,5,5,3,6,6,6,5,3,3,3,2,5,2)
UV<-c(6,6,7,8,5,6,5,6,6,6,7,7,8,8,5,6,8,5,7)
dat<-data.frame(Day,Group,Rain,UV)
library(rstatix)
library(tidyverse)
kt <- function(x, data) {
fmla <- as.formula(paste(x, "~ Group"))
data %>%
group_by(Day) %>%
kruskal_test(fmla)
}
lapply(c("Rain", "UV"), kt, data = dat) %>%
bind_rows()
#> # A tibble: 4 x 7
#> Day .y. n statistic df p method
#> <dbl> <chr> <int> <dbl> <int> <dbl> <chr>
#> 1 1 Rain 9 0.505 2 0.777 Kruskal-Wallis
#> 2 2 Rain 10 6.52 2 0.0384 Kruskal-Wallis
#> 3 1 UV 9 1.16 2 0.56 Kruskal-Wallis
#> 4 2 UV 10 0.423 2 0.809 Kruskal-Wallis