Write a function in R to extract the highest value of a variable in each data frame from a list of data frames

Question

I have a list of data frames:

df1 <- data.frame(day = c(1,2,3,4), price = c(100,120,90,22))
df2 <- data.frame(day = c(1,2,3,4,5,6,7), price = c(1,11,20,5,88,25,6))
my_list <- list(df1, df2)

I want to write a function which returns the max value of price and its corresponding day from both data frames.

Answer 1

In base R, we can use lapply -

lapply(my_list, function(x) x[which.max(x$price), ])

Or using dplyr and purrr -

library(dplyr)
library(purrr)

map(my_list, ~.x %>% slice(which.max(price)))

#[[1]]
#  day price
#1   2   120

#[[2]]
#  day price
#1   5    88