使用If从R中的列表中按名称选择数据框

Question

In R: I have a list of 3 dataframes (Book1, Book2, Book3), list named dflist4. I have a code I want to apply to each dataframe separately in the list because the value of maxm is different for each dataframe. I wrote it, and it works, but only when Book1, Book2, and Book3 are all equally sized dataframes. When they are not equally sized, the code will not run (error: ops.dataframe == only defined for equally-sized dataframes). When I change the == to = , i get that it is not logical. Can anyone please give a suggestion as to how to select the dataframes from the list based on their names no matter the size of the dataframe?

Code here:

eggplant<-function(x){
(if((x == (dflist4[["Book1"]])){
maxm = 3;
x %>% mutate(Col4 = (x[,3])/maxm);
})
(if((x == dflist4[["Book2"]])){
maxm = 2;
x %>% mutate(Col4 = (x[,3])/maxm);
})
(if((x == dflist4[["Book3"]])){
maxm = 1;
x %>% mutate(Col4 = (x[,3])/maxm);
})
}

test<-lapply(dflist4, eggplant)

Answer 1

Following up from my comments above, I assume the third column in Book1 , Book2 , Book3 is called Col3 .

You can use purrr::map2

library(tidyverse)
purrr::map2(dflist4, c(3, 2, 1), function(df, maxm) df %>% mutate(Col4 = Col3 / maxm))

---

As you don't provide sample data, here is an mtcars -based example

purrr::map2(list(mtcars[1:3, ], mtcars[1:3, ]), c(10, 100), function(df, maxm)
    df %>% mutate(mpg.new = mpg / maxm))
#[[1]]
#   mpg cyl disp  hp drat    wt  qsec vs am gear carb mpg.new
#1 21.0   6  160 110 3.90 2.620 16.46  0  1    4    4    2.10
#2 21.0   6  160 110 3.90 2.875 17.02  0  1    4    4    2.10
#3 22.8   4  108  93 3.85 2.320 18.61  1  1    4    1    2.28
#
#[[2]]
#   mpg cyl disp  hp drat    wt  qsec vs am gear carb mpg.new
#1 21.0   6  160 110 3.90 2.620 16.46  0  1    4    4   0.210
#2 21.0   6  160 110 3.90 2.875 17.02  0  1    4    4   0.210
#3 22.8   4  108  93 3.85 2.320 18.61  1  1    4    1   0.228