A data frame in R can be understood as tables with rows/columns.

Some R libraries such as ggplot2 only accept data frames, and we can use data.frame to convert a vector to a data frame:

data.frame(v)

The code above creates a data frame with a single column, but we can also use data.frame to create data frames with multiple columns. For instance:

month = 1:12
year = rep(2024, 12)
df = data.frame(month, year);
   month year
1      1 2024
2      2 2024
3      3 2024
4      4 2024
5      5 2024
6      6 2024
7      7 2024
8      8 2024
9      9 2024
10    10 2024
11    11 2024
12    12 2024