Difference between as.data.frame(x) and data.frame(x)

Question

What is the difference between as.data.frame(x) and data.frame(x)

In this following example, the result is the same at the exception of the columns names.

x <- matrix(data=rep(1,9),nrow=3,ncol=3) > x      [,1] [,2] [,3] [1,]    1    1    1 [2,]    1    1    1 [3,]    1    1    1 > data.frame(x)   X1 X2 X3 1  1  1  1 2  1  1  1 3  1  1  1 > as.data.frame(x)   V1 V2 V3 1  1  1  1 2  1  1  1 3  1  1  1 

Answer 1

As mentioned by Jaap, data.frame() calls as.data.frame() but there's a reason for it:

as.data.frame() is a method to coerce other objects to class data.frame. If you're writing your own package, you would store your method to convert an object of your_class under as.data.frame.your_class(). Here are just a few examples.

methods(as.data.frame)  [1] as.data.frame.AsIs            as.data.frame.Date             [3] as.data.frame.POSIXct         as.data.frame.POSIXlt          [5] as.data.frame.aovproj*        as.data.frame.array            [7] as.data.frame.character       as.data.frame.complex          [9] as.data.frame.data.frame      as.data.frame.default         [11] as.data.frame.difftime        as.data.frame.factor          [13] as.data.frame.ftable*         as.data.frame.integer         [15] as.data.frame.list            as.data.frame.logLik*         [17] as.data.frame.logical         as.data.frame.matrix          [19] as.data.frame.model.matrix    as.data.frame.numeric         [21] as.data.frame.numeric_version as.data.frame.ordered         [23] as.data.frame.raw             as.data.frame.table           [25] as.data.frame.ts              as.data.frame.vector              Non-visible functions are asterisked