How to extract certain columns from a list of data frames

Here's an example (this is the kind of thing you should have put in your question. You will get near-instantaneous help if you can structure your question with a clear, copy/pasteable, reproducible example like this.)

Problem:

# list of data frames:
l = list(mtcars, mtcars)

# vector of column names I would like to extract
my_names = c("mpg", "wt", "am")
# these columns might be at different positions in the data frames

Solution:

result = lapply(l, "[", , my_names)

# look at the top 6 rows of each to verify that it worked:
lapply(result, head)
# [[1]]
#                    mpg    wt am
# Mazda RX4         21.0 2.620  1
# Mazda RX4 Wag     21.0 2.875  1
# Datsun 710        22.8 2.320  1
# Hornet 4 Drive    21.4 3.215  0
# Hornet Sportabout 18.7 3.440  0
# Valiant           18.1 3.460  0
#
# [[2]]
#                    mpg    wt am
# Mazda RX4         21.0 2.620  1
# Mazda RX4 Wag     21.0 2.875  1
# Datsun 710        22.8 2.320  1
# Hornet 4 Drive    21.4 3.215  0
# Hornet Sportabout 18.7 3.440  0
# Valiant           18.1 3.460  0

Explanation: You essentially want to do l[[1]][, my_names], l[[2]][, my_names], ... lapply applies a function to every list element. In this case, the function is [, which takes rows as its first argument (we leave it blank to indicate all rows), columns as its second argument (we give it my_names). It returns the results in a list.

You can use dplyr, it is nice, easy and the syntax is clear:

    library(dplyr)
    l <- list(mtcars, mtcars) # the list of 2 df
    new_list <- lapply(l, function(x) x%>% select(mpg,wt,am))

Ciao!