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

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