difficulty with naming dataframe using loop, rbind and list of dataframe names

Question

I am a new R programmer. I am trying to use rbind to combine temporary data frames. I need the names of each set of combined datasets to come from a list of data frames that a loop iterates through.

I can get the temporary files to combine properly, but it doesn't work if I use the data frame name from iterating through the name list. I have searched and searched and also called a programmer friend, to no avail. Thank you!!

#initialize empty data frames
sheet1 <- data.frame(County = character(), Winner = character())
sheet2 <- data.frame(County = character(), Winner = character())
sheet3 <- data.frame(County = character(), Winner = character())
sheet4 <- data.frame(County = character(), Winner = character())

#put empty data frames into a list
sheet_dfs <- c(sheet1, sheet2, sheet3, sheet4)

#pull information from different Excel sheets for each iteration (not shown here)
#and write to element of list of dataframes 
for (i in 1:3) {
  temp1 <- data.frame(c("Cobb","Clayton","Fulton"), c("Kemp","Abrams","Smith"))
  colnames(temp1) <- c("County","Winner")
  temp2 <- data.frame(c("Henry","Polk","Gwinnett"), c("Fuller","Parker","Newsome"))
  colnames(temp2) <- c("County","Winner")
  sheet_dfs[[i]] <- rbind(temp1,temp2)}

sheet1 #expecting a data frame with names, what am I doing wrong?
sheet2 #expecting a data frame with names, what am I doing wrong?
sheet3 #expecting a data frame with names, what am I doing wrong?

test <- rbind(temp1,temp2)
test #this is exactly the output I need for my dataframes sheet1,sheet2,sheet3. 
returns:
County  Winner
1     Cobb    Kemp
2  Clayton  Abrams
3   Fulton   Smith
4    Henry  Fuller
5     Polk  Parker
6 Gwinnett Newsome

Once objects are saved to a list their original sources are not connected and remain as separate objects. The sheets data frames are never reassigned values so they remain empty. — Parfait
– Parfait, Commented Dec 31, 2018 at 21:26
You've only modified the contents of sheet_dfs but not sheet1, sheet2, or sheet3. You'll notice that names(sheet_dfs) doesn't even relate back to sheet1... — svenhalvorson
– svenhalvorson, Commented Dec 31, 2018 at 21:29
Is there a way to name these dataframes that I am creating using the "i" from the loop? — JenniferAnn
– JenniferAnn, Commented Dec 31, 2018 at 21:30

Manuel Bickel · Accepted Answer · 2019-01-01 09:12:34Z

First, you need to create a proper named list. Your initial list assignment just creates a vector via c. Furthermore, you need to access the list elements properly via [[ or name. See below modification of your code.

# set up named list programmatically
sheet_names = paste0("sheet", 1:4)
sheet_dfs = setNames(vector(length = length(sheet_names), mode = "list"), sheet_names)
# you can also create a named list as follows, which is, however, less programmatically
# sheet_dfs = list("sheet1" = sheet1, "sheet2" = sheet2, ...)

# your temp assignments...
#pull information from different Excel sheets for each iteration (not shown here)
#and write to element of list of dataframes 
for (i in 1:3) {
  temp1 <- data.frame(County = c("Cobb","Clayton","Fulton"), Winner = c("Kemp","Abrams","Smith"))
  temp2 <- data.frame(County = c("Henry","Polk","Gwinnett"), Winner = c("Fuller","Parker","Newsome"))
  sheet_dfs[[i]] <- rbind(temp1,temp2)
}

# access the list via name or index
sheet_dfs[[1]]
sheet_dfs["sheet1"]

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