How to remove all rows in R that have a specific month?

Question

I have a data.frame where in one column I have a lot of different dates in the format Year-Month-Day and I would like to keep only the rows that have as a month 12, so December.

I tried two different codes:

First version:

IBES1985_1990[IBES1985_1990$`Forecast Period End Date, SAS Format` != 
                month(1,2,3,4,5,6,7,8,9,10,11, )] 

But here I get an error saying that undefined columns where selected.

Second version:

IBES1985_1990 <- IBES1985_1990 %>%
  mutate(`Forecast Period End Date, SAS Format`= ifelse(month(`Forecast Period End Date, SAS Format`)
         %in% c(1,2,3,4,5,6,7,8,9,10,11),NA,`Forecast Period End Date, SAS Format`))

Here I wanted to then delete all the rows that have NA in it but the date format changed to pure numbers and I couldn't change it back to see if I the dates that don't have December were already deleted or not.

In summary, I would like to have a code where all rows are deleted that are not December.

Answer 1

If your data looks like this

library(lubridate)

df <- data.frame(dates = seq.Date(ymd("2022-09-02"), ymd("2023-02-02"), "month"), 
  data = 1:6)
df
       dates data
1 2022-09-02    1
2 2022-10-02    2
3 2022-11-02    3
4 2022-12-02    4
5 2023-01-02    5
6 2023-02-02    6

keep all December dates e.g. by using strftime

df[strftime(df$dates, format="%b") == "Dec", ]
       dates data
4 2022-12-02    4

With dplyr you can do

library(dplyr)

df %>% 
  rowwise() %>% 
  summarize(dates = dates[strftime(dates, format="%b") == "Dec"], data)
# A tibble: 1 × 2
  dates       data
  <date>     <int>
1 2022-12-02     4

or, if you want to use lubridates month

library(dplyr)
library(lubridate)

df %>% 
  rowwise() %>% 
  summarize(dates = dates[month(dates) == 12], data)
# A tibble: 1 × 2
  dates       data
  <date>     <int>
1 2022-12-02     4