How to make a data.frame with 1 row 0 column?

Question

R> data.frame()
data frame with 0 columns and 0 rows

I can make the above data.frame with 0 row and 0 column. How to make a data.frame with 1 row and 0 column?

EDIT: It is absolutely useful, as shown in the following use case.

R> data.frame(data.frame(), y=1)
Error in data.frame(data.frame(), y = 1) :
  arguments imply differing number of rows: 0, 1
R> data.frame(data.frame(x=1)[,0,drop=F], y=1)
  y
1 1

You can't have a row without a column I'm afraid. data.frames in R are a list of column vectors. "rows" are just slides across those column vectors. Why are you trying to create such an object? — MrFlick
– MrFlick, Commented Aug 16, 2021 at 6:17
I have upvoted this question because it's about an object that shouldn't be deliberately created, like @MrFlick says. — Rui Barradas
– Rui Barradas, Commented Aug 16, 2021 at 7:13

Miff · Accepted Answer · 2021-08-16 06:28:22Z

5

This can be done by making a one by one data.frame and selecting the first zero columns:

data.frame(x=1)[,0,drop=FALSE]
#data frame with 0 columns and 1 row

Check that this does have the right dimensions:

dim(data.frame(x=1)[,0,drop=FALSE])
#[1] 1 0

answered Aug 16, 2021 at 6:28

Miff

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2 Comments

AEF Over a year ago

Interesting. But note the result does no longer function as a usual dataframe. E.g. rbind(data.frame(x=1)[,0,drop=FALSE], data.frame(x=1)[,0,drop=FALSE]) gives a dataframe with 0 rows instead of two rows as you would expect. I think this is because your structure has one rowonly because of the row.names attribute and not because of content.

user15502206 Over a year ago

I think that it is just a bug in R.

user15502206 · Accepted Answer · 2021-08-16 11:47:41Z

0

This is an alternative solution.

nrow=1 # this can be tuned to return n rows 0 column data.frame.
structure(data.frame(), row.names = seq(nrow))

answered Aug 16, 2021 at 11:47

user15502206

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