What is the difference between as.tibble(), as_data_frame(), and tbl_df()?

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I remember reading somewhere that as.tibble() is an alias for as_data_frame(), but I don't know what exactly an alias is in programming terminology. Is it similar to a wrapper?

So I guess my question probably comes down to the difference in possible usages between tbl_df() and as_data_frame(): what are the differences between them, if any?

More specifically, given a (non-tibble) data frame df, I often turn it into a tibble by using:

df <- tbl_df(df)

Wouldn't 

df <- as_data_frame(df)

do the same thing? If so, are there other cases where the two functions tbl_df() and as_data_frame() can not be used interchangeably to get the same result?

The R documentation says that

tbl_df() forwards the argument to as_data_frame()

does that mean that tbl_df() is a wrapper or alias for as_data_frame()? R documentation doesn't seem to say anything about as.tibble() and I forgot where I read that it was an alias for as_data_frame(). Also, apparently as_tibble() is another alias for as_data_frame().

If these four functions really are all the same function, what is the sense in giving one function four different names? Isn't that more confusing than helpful?

tibble dplyr tidyverse r terminology
2 Answers

According to the introduction to tibble, it seems like tibbles supersede tbl_df.

I’m pleased to announce tibble, a new package for manipulating and printing data frames in R. Tibbles are a modern reimagining of the data.frame, keeping what time has proven to be effective, and throwing out what is not. The name comes from dplyr: originally you created these objects with tbl_df(), which was most easily pronounced as “tibble diff”.

[...]This package extracts out the tbl_df class associated functions from dplyr.

To add to the confusion, tbl_df now calls as_tibble, which is the preferred alias for as_data_frame and as.tibble: (Hadley Wickham's comment on the issue, and as_tibble docs)

> tbl_df
function (data) 
{
    as_tibble(data, .name_repair = "check_unique")
}

According to the help description of tbl_df(), it is deprecated and tibble::as_tibble() should be used instead. as_data_frame and as.tibble help pages both redirect to as_tibble.

When calling class on a tibble, the class name still shows up as tbl_df:

> as_tibble(mtcars) %>% class
[1] "tbl_df"     "tbl"        "data.frame"
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