Data Frame Suddenly Turned into a Tibble

[Anisha]

I'm still fairly new to tibbles and had a question about it.
I was mutating a data frame to include new columns, and it suddenly turned into a tibble. Is there a reason why this happened?

I have the code below - the combined_dataframe was a regular data frame, but the resulting tf_idf ended up being a tibble:

tf_idf <- combined_dataframe %>% 
  add_count(word) %>%
  group_by(source) %>%
  mutate("IDF" = 1 + log(3 / n)) %>%
  mutate("TF_IDF" = TF * IDF) 

[technocrat]

Sharp eyes. This is simply a consequence of the design decisions for the dplyr::group_by() function.

suppressPackageStartupMessages(library(dplyr))
class(mtcars)
#> [1] "data.frame"
mtcars %>% group_by(mpg) -> obj
class(obj)
#> [1] "grouped_df" "tbl_df"     "tbl"        "data.frame"
obj
#> # A tibble: 32 x 11
#> # Groups:   mpg [25]
#>      mpg   cyl  disp    hp  drat    wt  qsec    vs    am  gear  carb
#>  * <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
#>  1  21       6  160    110  3.9   2.62  16.5     0     1     4     4
#>  2  21       6  160    110  3.9   2.88  17.0     0     1     4     4
#>  3  22.8     4  108     93  3.85  2.32  18.6     1     1     4     1
#>  4  21.4     6  258    110  3.08  3.22  19.4     1     0     3     1
#>  5  18.7     8  360    175  3.15  3.44  17.0     0     0     3     2
#>  6  18.1     6  225    105  2.76  3.46  20.2     1     0     3     1
#>  7  14.3     8  360    245  3.21  3.57  15.8     0     0     3     4
#>  8  24.4     4  147.    62  3.69  3.19  20       1     0     4     2
#>  9  22.8     4  141.    95  3.92  3.15  22.9     1     0     4     2
#> 10  19.2     6  168.   123  3.92  3.44  18.3     1     0     4     4
#> # … with 22 more rows

^{Created on 2020-03-23 by the reprex package (v0.3.0)}

[Anisha]

@technocrat thank you for clearing that up for me!