Using R to mutate columns based on the value of another column

Question

I'm basically trying to mutate a data set and add a column based on the value of another column in that dataset. How do I do this?

Say I have a data set that looks like this:

movies
# A tibble: 651 x 32
                    title   title_type       genre runtime mpaa_rating                   studio
                    <chr>       <fctr>      <fctr>   <dbl>      <fctr>                   <fctr>
 1            Filly Brown Feature Film       Drama      80           R      Indomina Media Inc.
 2               The Dish Feature Film       Drama     101       PG-13    Warner Bros. Pictures
 3    Waiting for Guffman Feature Film      Comedy      84           R   Sony Pictures Classics
 4   The Age of Innocence Feature Film       Drama     139          PG        Columbia Pictures
 ... (more columns and more rows than shown)

Say it has a column (not shown) called thtr_release_month with possible values equal to a month of the year like "October" or "January"

I want to add a column called oscar_season that is either yes or no if the movie was released in November or December. How does one do this? I feel like this is close:

movies_with_oscar_season <- movies %>% mutate(oscar_season = ifelse(movies$thtr_release_month == 'November' | movies$thtr_release_month == 'December', 'yes', 'no'))

What am I missing? How can I improve the above code?

I actually get an error:

Column oscar_season must be length 651 (the number of rows) or one, not 0 Calls: <Anonymous> ... <Anonymous> -> mutate -> mutate.tbl_df

What am I doing wrong?

Is there a way to write that long or expression too?

Always provide a [minimal reproducible example](https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example). — M--, Nov 07 '17 at 18:24
What you want is to add a new column with the value `TRUE` if `thtr_release_month` is `November` or `December`, right? — Alejandro Montilla, Nov 07 '17 at 18:32

Alejandro Montilla · Accepted Answer · 2017-11-07T20:20:24.050

2

You can create a new vector with the result of evaluating your condition:

oscar_season <- (ifelse(movies$thtr_release_month %in% c('November','December')), "yes", "no")

Edit: Based on the comments, it is required to show a "yes" or a "no" if the condicion is TRUE or FALSE respectively.

And then call mutate with that new column:

movies_oscar_season <- mutate(movies, oscar_season)

That should give you the original dataset with the oscar_season column.

edited Nov 07 '17 at 20:20

answered Nov 07 '17 at 18:40

Alejandro Montilla

2,626
3
31
35

Is there another way to write this that is more concise: `(movies$thtr_release_month == 'November') | (movies$thtr_release_month == 'December')` – Jwan622 Nov 07 '17 at 19:59
Do you mean something like `oscar_season <- (movies$thtr_release_month %in% c("November","December") ) ` ? – Alejandro Montilla Nov 07 '17 at 20:04
@Jwan622 Take a look at my answer now, I've edit it to a more concise condition and to replace Booleans with "yes" or "no". – Alejandro Montilla Nov 07 '17 at 20:22

Using R to mutate columns based on the value of another column

1 Answers1

Linked