Creating season variable by month with dplyr in R

Question

I have a dataset that has a variable called month, which each month as a character. Is there a way with dplyr to combine some months to create a season variable? I have trie

Answer 1

When there are multiple key/value, we can do a join with a key/val dataset

keyval <- data.frame(month = month.abb, 
      season = rep(c("Winter", "Spring", "Summer", "Fall"), each = 3),
      stringsAsFactors = FALSE)

left_join(data, keyval)

Answer 2

The correct syntax should be

data %>% mutate(season = ifelse(month %in% 10:12, "Fall",
                               ifelse(month %in% 1:3, "Winter",
                                      ifelse(month %in% 4:6, "Spring",
                                             "Summer"))))

Edit: probably a better way to get the job done

Astronomical Seasons

temp_data %>%
  mutate(
    season = case_when(
      month %in% 10:12 ~ "Fall",
      month %in%  1:3  ~ "Winter",
      month %in%  4:6  ~ "Spring",
      TRUE ~ "Summer"))

Meteorological Seasons

temp_data %>%
  mutate(
    season = case_when(
      month %in%  9:11 ~ "Fall",
      month %in%  c(12, 1, 2)  ~ "Winter",
      month %in%  3:5  ~ "Spring",
      TRUE ~ "Summer"))

Answer 3

You can also try using dplyr::recode or functions from forcats. I think this is the simplest method here:

library(tidyverse)
library(lubridate)
#> 
#> Attaching package: 'lubridate'
#> The following object is masked from 'package:base':
#> 
#>     date
data <- tibble(month = c("Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"))

data %>%
  mutate(
    season = fct_collapse(
      .f = month,
      Spring = c("Mar", "Apr", "May"),
      Summer = c("Jun", "Jul", "Aug"),
      Autumn = c("Sep", "Oct", "Nov"),
      Winter = c("Dec", "Jan", "Feb")
    )
  )
#> # A tibble: 12 x 2
#>    month season
#>    <chr> <fct> 
#>  1 Jan   Winter
#>  2 Feb   Winter
#>  3 Mar   Spring
#>  4 Apr   Spring
#>  5 May   Spring
#>  6 Jun   Summer
#>  7 Jul   Summer
#>  8 Aug   Summer
#>  9 Sep   Autumn
#> 10 Oct   Autumn
#> 11 Nov   Autumn
#> 12 Dec   Winter

Created on 2018-04-06 by the reprex package (v0.2.0).