R - assign inside a for loop using existing name

Question

I want to do the same manipulation to each element in a list of data frames using a for loop. I then want to assign the name of these using the original name of the element. I'd like to know how to do this in the case where I just reassign with the same name, or assign with the old name with a suffix or prefix.

I can do it by adding new names with paste0, for example:

# load example data frames and add to list
data("iris")
data("cars")+
list_df <- list(iris, cars)

# create new list for manipulated data frames. Using head() as an example.
list_head < - list()

# for loop to take head of each data frame in list_df, assign iterative name and add to list_head
for (i in 1:length(list_df){
   temp <- head(list_df[[i]])
   new_list[[paste0("df_head",i)]] <- temp
}

I want to be able to assign a variable within a loop based on the iteration, where the names assigned are the same as the old names, and/or with the old name plus a suffix/prefix, e.g. "cars_head". The adding to a list part isn't important, although if that can be done straightforwardly as well that would be great.

Wimpel · Accepted Answer · 2022-03-29 10:50:24Z

1

I think this is a more R-like approach...

data("iris")
data("cars")

library(tibble)
#create a list with names of the elements
list_df <- tibble::lst(iris, cars)
#get head of list's elements
new_list <- lapply(list_df, head)
#new names
names(new_list) <- paste0(names(list_df), "_head")

new_list
# $iris_head
# Sepal.Length Sepal.Width Petal.Length Petal.Width Species
# 1          5.1         3.5          1.4         0.2  setosa
# 2          4.9         3.0          1.4         0.2  setosa
# 3          4.7         3.2          1.3         0.2  setosa
# 4          4.6         3.1          1.5         0.2  setosa
# 5          5.0         3.6          1.4         0.2  setosa
# 6          5.4         3.9          1.7         0.4  setosa
# 
# $cars_head
# speed dist
# 1     4    2
# 2     4   10
# 3     7    4
# 4     7   22
# 5     8   16
# 6     9   10

answered Mar 29, 2022 at 10:50

Wimpel

27.9k1 gold badge25 silver badges40 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Dee G Over a year ago

Would this work for a much more involved set of manipulations than just taking the head? I'm still not familiar with lapply, sapply, etc..

Wimpel Over a year ago

yes it would... lapply(mylist, function(x) { ... whatever you want to do with element x .. }) would work

Dee G Over a year ago

Even multiple steps, e.g., take rows which meet a certain condition, mutate to create new column based on another column, gather the result, etc. ?

Wimpel Over a year ago

sure.. I can't see why not. Just remember that the last line defines the output, or use return().

Collectives™ on Stack Overflow

R - assign inside a for loop using existing name

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related