使用rbind合并data.tables时出错，其中之一为空

Question

An error is issued when merging three (or more) data.tables with rbind and there is an empty data.table between two non-empty data.tables:

> require(data.table)
Loading required package: data.table
data.table 1.9.2  For help type: help("data.table")

> DT <- data.table(x=c(1,2,3))
> rbind(DT, data.table(), DT)
Error in setcolorder(tt, chmatch(match.names, make.names(original.names[[x]],  (from <text>#1) : 
  Column numbers in neworder out of bounds: NA

This does not happen if the empty data.table is in the end:

> rbind(DT, DT, data.table()) 
   x
1: 1
2: 2
3: 3
4: 1
5: 2
6: 3

But some other error happens when the empty data.table is in the beginning:

> rbind(data.table(), DT, DT) 
Error in data.table::.rbind.data.table(...) (from <text>#1) : 
  Some colnames of argument 2 (x) are not present in colnames of item 1. If an argument has colnames they can be in a different order, but they must all be present. Alternatively, you can supply unnamed lists and they will then be joined by position. Or, set use.names=FALSE.

However, if we use only two arguments everything is fine:

> rbind(data.table(), DT) 
   x
1: 1
2: 2
3: 3

What should be the expected behavior?

Answer 1

This seems to be due to inconsistent behavior in data.table::.rbind.data.table . Adding the following line would fix this. Please file a bug-report with the data.table developers.

....
original.names = lapply(list(...), names)
allargs = lapply(list(...), as.data.table)
original.names = original.names[sapply(allargs, length) > 0L]  # this is the new line
allargs = allargs[sapply(allargs, length) > 0L]
...

Answer 2

Bug #5612 is now fixed in commit #1266 (v1.9.3). From NEWS :

o Implementing #5249 closes bug #5612 , a case where rbind gave error when binding with empty data.tables as shown here: Error when using rbind to merge data.tables and one of them is empty . Thanks to Roger for reporting on SO.

Now, the line:

> rbind(data.table(), DT, DT) 

gives:

#    x
# 1: 1
# 2: 2
# 3: 3
# 4: 1
# 5: 2
# 6: 3