Convert named vector to dataframe

I'd do something like this:

res = data.frame(cbind(do.call('rbind', strsplit(names(x), " ")), x))
res
     V1 V2 x
0 15  0 15 1
1 15  1 15 2
2 15  2 15 3
0 16  0 16 4
1 16  1 16 5

Do mind that the data types are not correct yet, the first two columns are factor's.

Here's a very direct approach:

cbind(read.table(text = names(x)), x)
     V1 V2 x
0 15  0 15 1
1 15  1 15 2
2 15  2 15 3
0 16  0 16 4
1 16  1 16 5

In this case, read.table will automatically take care of splitting your names(x) component (by default, by space, but other characters could be specified if necessary).

You can also set the name for x directly in cbind:

cbind(read.table(text = names(x)), V3 = x)

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A more direct approach would be to use cSplit from my "splitstackshape" package, like this:

library(splitstackshape)
cSplit(stack(x), "ind", " ")