通过数据帧循环子集

Question

i have 20 data frames of which i would like to subset 4 variables into a new data frame.

DF1 <- subset(Circle1.csv, select = c(col1, col2, col3, col4))
DF2 <- subset(Circle2.csv, select = c(col1, col2, col3, col4))

I don't want to write this out 20 times; is there a way of looping this ?

many thanks

Answer 1

Get all the objects into a list , and subset it once by looping over the list

lst1 <- lapply(mget(sprintf("Circle%d.csv", 1:20)), subset, 
            select = c(col1, col2, col3, col4))

---

Or with dplyr/purrr

library(purrr)
library(dplyr)
lst1 <- map(mget(sprintf("Circle%d.csv", 1:20)), ~ .x %>% 
                      select(col1:col4))

Answer 2

using for loop

nrows <- 1:4 # number of rows to subset
colNames <- c('col1', 'col2', 'col3', 'col4') # column names

# assign subset of dataframe
for (i in 1:20) {
  assign(x = paste0('DF', i), value = get(paste0('Circle', i, '.csv'))[nrows, colNames])
}