[R] Inconsistency in 'names' when calling data.frame on other data.frames

[Rui Barradas]

Hello,

Yes, this is documented. From ?data.frame, section Value

How the names of the data frame are created is complex, and the rest
of this paragraph is only the basic story. [...]
For a named matrix/list/data frame argument with more than one named
column, the names of the columns are the name of the argument followed
by a dot and the column name inside the argument: if the argument is
unnamed, the argument's column names are used.
[...]


You can protect data.frame's arguments with I(). Compare the two calls below.


df1 <- data.frame(a = data.frame(A = 1, C = 1), b = data.frame(B = 1, D = 1))
str(df1)
#> 'data.frame':    1 obs. of  4 variables:
#>  $ a.A: num 1
#>  $ a.C: num 1
#>  $ b.B: num 1
#>  $ b.D: num 1
names(df1)
#> [1] "a.A" "a.C" "b.B" "b.D"

df2 <- data.frame(a = I(data.frame(A = 1, C = 1)), b = I(data.frame(B
= 1, D = 1)))
str(df2)
#> 'data.frame':    1 obs. of  2 variables:
#>  $ a:Classes 'AsIs' and 'data.frame':    1 obs. of  2 variables:
#>   ..$ A: num 1
#>   ..$ C: num 1
#>  $ b:Classes 'AsIs' and 'data.frame':    1 obs. of  2 variables:
#>   ..$ B: num 1
#>   ..$ D: num 1
names(df2)
#> [1] "a" "b"
df2  # the names come from the print method
#>   a.A a.C b.B b.D
#> 1   1   1   1   1


Hope this helps,

Rui Barradas



Peter Langfelder <peter.langfelder using gmail.com> escreveu (sexta,
21/08/2026 à(s) 17:01):
>
> Hi all,
>
> when calling data.frame on other data frames and naming arguments, the
> way the 'names' of the result are formed seems to depend on whether
> the argument data frames have one or more columns. Specifically,
> consider this:
>
> > data.frame(a = data.frame(A = 1), b = data.frame(B = 1))
>   A B
> 1 1 1
>
>
> Here the column names are simply copied from column names of the arguments.
> In contrast, if the argument data frames have two (or more) columns,
> here's what happens:
>
> > data.frame(a = data.frame(A = 1, C = 1), b = data.frame(B = 1, D = 1))
>   a.A a.C b.B b.D
> 1   1   1   1   1
>
>
> The 'names' of the result are now <name of the argument>.<column name
> of the argument value>
>
> Is this behavior intended?
>
> Thanks,
>
> Peter
>
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