When filtering with dates "%in%" and "==" are behaving differently

I am trying to filter a dataframe based on a date column having values in a select vector of dates. When I filter using "%in%", I get no rows returned, however when I filter with "==" on a given element I do get rows returned.

Here is a sample data:

library(lubridate)
library(dplyr)

samp_df = data.frame(epoch = c(1671916189, 1652728555, 1657658906, 1662514742, 1670702851)) %>%
	mutate(dt = as.POSIXct(epoch, origin = '1970-01-01', tz = 'America/Phoenix')) %>%
	mutate(month = floor_date(dt, 'month'))
samp_df

       epoch                  dt      month
# 1 1671916189 2022-12-24 14:09:49 2022-12-01
# 2 1652728555 2022-05-16 12:15:55 2022-05-01
# 3 1657658906 2022-07-12 13:48:26 2022-07-01
# 4 1662514742 2022-09-06 18:39:02 2022-09-01
# 5 1670702851 2022-12-10 13:07:31 2022-12-01

months_to_check = c(as.Date('2022-12-01', tz = 'America/Phoenix'),
	            as.Date('2022-05-01', tz = 'America/Phoenix'))

months_to_check

# [1] "2022-12-01" "2022-05-01"

The following code returns no rows:

samp_df %>%
	filter(month %in% months_to_check)

However, the following code does return rows:

samp_df %>%
	filter(month == months_to_check[1])

Why is there this discrepancy?

The "month" variable is a "POSIXct" (you created it based on dt), while months_to_check is a "Date". Even if they print similar, they are not the same.

But, the "lubridate" package adds a special method to == that has a workaround to that. We can pull the code of this method with:

sloop::s3_get_method('==.POSIXt')

The code for the method is at the end of this answer, but see that we convert one date to the same format as the other, before doing the logical comparison, that is why you get matches with ==.

But %in% doesn't have that, it doesn't convert the formats, thus not returning any matches.

The solution is quite simple, just keep a consistent date formatting across your variables, which you should always do, to avoid this type of error.

Code for `==.POSIXt`:

function (e1, e2) 
{
    if (nargs() == 1) {
        stop(gettextf("unary '%s' not defined for \"%s\" objects", 
            .Generic, class(e1)), domain = NA)
    }
    if (inherits(e1, "POSIXlt")) {
        e1 <- as.POSIXct(e1)
    }
    if (inherits(e2, "POSIXlt")) {
        e2 <- as.POSIXct(e2)
    }
    if (is.character(e1)) { #here
        e1 <- if (is.Date(e2)) {
            as.Date(e1)
        }
        else {
            as.POSIXct(e1)
        }
    }
    if (is.character(e2)) { #here
        e2 <- if (is.Date(e1)) {
            as.Date(e2)
        }
        else {
            as.POSIXct(e2)
        }
    }
    if (is.POSIXct(e1) && is.Date(e2)) {
        e2 <- date_to_posix(e2, tz(e1))
        base::check_tzones(e1, e2)
    }
    else if (is.Date(e1) && is.POSIXct(e2)) {
        e1 <- date_to_posix(e1, tz = tz(e2))
        base::check_tzones(e1, e2)
    }
    NextMethod(.Generic)
}