How I can use the function names with for in R - r

Question

I have a little problem with my R code. I don't know where, but I make a mistake.
The problem is:
I have many file excel with the same names of the columns. I'd like to change the titles of the matrix, with a other titles.
These are five files.
AA <- read_excel("AA.xlsx")
BB <- read_excel("BB.xlsx")
CC <- read_excel("CC.xlsx")
DD <- read_excel("DD.xlsx")
EE <- read_excel("EE.xlsx")
head(AA) #the matrix is the same for the other file.
DATA Open Max Min Close VAR % CLOSE VOLUME
<dttm> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
1 2004-07-07 00:00:00 3.73 3.79 3.6 3.70 0 21810440
2 2004-07-08 00:00:00 3.7 3.71 3.47 3.65 -1.43 7226890
3 2004-07-09 00:00:00 3.61 3.65 3.56 3.65 0 3754407
4 2004-07-12 00:00:00 3.64 3.65 3.59 3.63 -0.55 850667
5 2004-07-13 00:00:00 3.63 3.63 3.58 3.59 -1.16 777508
6 2004-07-14 00:00:00 3.54 3.59 3.47 3.5 -2.45 1931765
To change the titles fast, I decided to use this code.
t <- list(AA, BB, CC, DD, EE)
for (i in t ) {
names(i) <- c("DATA", "OPE", "MAX", "MIN", "CLO", "VAR%", "VOL")
} #R dosen't give any type of error!
head(AA) #the data are the same, as the for dosen't exits.
Where I was wrong?
Thank you so much in advance.
Francesco

Answer 1

We can do this with lapply. Get the datasets in a list with mget, loop through the list, set the column names to vector of names ('nm1
) and modify the objects in the global environment with list2env
nm1 <- c("DATA", "OPE", "MAX", "MIN", "CLO", "VAR%", "VOL")
lst <- lapply(mget(nm2), setNames, nm1)
list2env(lst, envir = .GlobalEnv)
Or using a for loop, loop through the string of object names and assign the column names to the objects in the global environment
for(nm in nm2) assign(nm, `names<-`(get(nm), nm1))
Or using tidyverse
library(tidyverse)
mget(nm2) %>%
map(set_names, nm1) %>%
list2env(., envir = .GlobalEnv)
data
AA <- mtcars[1:7]
BB <- mtcars[1:7]
CC <- mtcars[1:7]
DD <- mtcars[1:7]
EE <- mtcars[1:7]
nm2 <- strrep(LETTERS[1:5], 2)

Answer 2

I am trying to explain why your code didn't work. In the list t, the address of AA (t[[1]]) is the the same as AA in the global environment. In the for-loop, i initially is the same copy as the data.frame AA in global env. When you change the names of i with names(i) <-, the data.frame i is copied twice. Finally, you are changing the name of a new data.frame i rather than the original data.frame AA in the global environment.
Here is an example to illustrate what I mean (tracemem "marks an object so that a message is printed whenever the internal code copies the object."):
tracemem(mtcars)
# [1] "<0x1095b2150>"
tracemem(iris)
# [1] "<0x10959a350>"
x <- list(mtcars, iris)
for(i in x){
cat('-------\n')
tracemem(i)
names(i) <- paste(names(i), 'xx')
}
# -------
# tracemem[0x1095b2150 -> 0x10d678c00]:
# tracemem[0x10d678c00 -> 0x10d678ca8]:
# -------
# tracemem[0x10959a350 -> 0x10cb307b0]:
# tracemem[0x10cb307b0 -> 0x10cb30818]: