rdataframetibblename-value

Why does add_column assign a letter to the data?

I tried reading through R's documentation on the add_column function, but I'm a little confused as to the examples it provides. See below:

# add_column ---------------------------------
df <- tibble(x = 1:3, y = 3:1)

df %>% add_column(z = -1:1, w = 0)
df %>% add_column(z = -1:1, .before = "y")

# You can't overwrite existing columns
try(df %>% add_column(x = 4:6))

# You can't create new observations
try(df %>% add_column(z = 1:5))

What is the purpose of these letters that are being assigned a range? Eg:

z = 1:5

My understanding from the documentation is that add_column() takes in a dataframe and appends it in position based on the .before and .after arguments defaulting to the end of the dataframe.

I'm a little confused here. There is also a "..." argument that takes in Name-value pairs. Is that what I'm seeing with "z = 1:5"? What is the functional purpose of this?

Solution

  • data.frame columns always have a name in R, no exception.

    Since add_column adds new columns, you need to specify names for these columns.

    … well, technically you don’t need to. The following works:

    df %>% add_column(1 : 3)

    But add_column auto-generates the column name based on the expression you pass it, and you might not like the result (in this case, it’s literally 1:3, which isn’t a convenient name to work with).

    Conversely, the following also works and is perfectly sensible:

    z = 1 : 3
df %>% add_column(z)

    Result:

    # A tibble: 3 x 3
      x     y     z
  <int> <int> <int>
1     1     3     1
2     2     2     2
3     3     1     3