rbind data.frames without names

dataframe, names, r, rbind

Solution

Because `unname()` & explicitly assigning NA as column headers are not identical actions. When the column names are all NA, then an `rbind()` is possible. Since `rbind()` takes the names/colnames of the data frame, the results do not match & hence `rbind()` fails.

Here is some code to help see what I mean:

> c1 <- c(1,2,3)
> c2 <- c('A','B','C')
> df1 <- data.frame(c1,c2)
> df1
  c1 c2
1  1  A
2  2  B
3  3  C
> df2 <- data.frame(c1,c2) # df1 & df2 are identical
>
> #Let's perform unname on one data frame &
> #replacement with NA on the other
>
> unname(df1)
  NA NA
1  1  A
2  2  B
3  3  C
> tem1 <- names(unname(df1))
> tem1
NULL
>
> #Please note above that the column headers though showing as NA are null
>
> names(df2) <- rep(NA,ncol(df2))
> df2
  NA NA
1  1  A
2  2  B
3  3  C
> tem2 <- names(df2)
> tem2
[1] NA NA
> 
> #Though unname(df1) & df2 look identical, they aren't
> #Also note difference in tem1 & tem2
>
> identical(unname(df1),df2)
[1] FALSE
>

I hope this helps. The names show up as `NA` each, but the two operations are different.

Hence, two data frames with their column headers replaced to `NA` can be "rbound" but two data frames without any column headers (achieved using `unname()`) cannot.

Problem

I am trying to figure out why the `rbind` function is not working as intended when joining data.frames without names. Here is my testing: ``` test <- data.frame( id=rep(c("a","b"),each=3), time=rep(1:3,2), black=1:6, white=1:6, stringsAsFactors=FALSE ) # take some subsets with different names pt1 <- test[,c(1,2,3)] pt2 <- test[,c(1,2,4)] # method 1 - rename to same names - works names(pt2) <- names(pt1) rbind(pt1,pt2) # method 2 - works - even with duplicate names names(pt1) <- letters[c(1,1,1)] names(pt2) <- letters[c(1,1,1)] rbind(pt1,pt2) # method 3 - works - with a vector of NA's as names names(pt1) <- rep(NA,ncol(pt1)) names(pt2) <- rep(NA,ncol(pt2)) rbind(pt1,pt2) # method 4 - but... does not work without names at all? pt1 <- unname(pt1) pt2 <- unname(pt2) rbind(pt1,pt2) ``` This seems a bit odd to me. Am I missing a good reason why this shouldn't work out of the box? edit for additional info Using @JoshO'Brien's suggestion to `debug`, I can identify the error as occurring during this `if` statement part of the `rbind.data.frame` function ``` if (is.null(pi) || is.na(jj <- pi[[j]])) ``` (online version of code here: http://svn.r-project.org/R/trunk/src/library/base/R/dataframe.R starting at: "### Here are the methods for rbind and cbind.") From stepping through the program, the value of `pi` does not appear to have been set at this point, hence the program tries to index the built-in constant `pi` like `pi[[3]]` and errors out. From what I can figure, the internal `pi` object doesn't appear to be set due to this earlier line where `clabs` has been initialized as `NULL`: ``` if (is.null(clabs)) clabs <- names(xi) else { #pi gets set here ``` I am in a tangle trying to figure this out, but will update as it comes together.

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