Conditionally mutate column across list of dataframes in R - r

Question

I am working with a large list of dataframes that use inconsistent date formats. I would like to conditionally mutate across the list so that any dataframe that contains a string will use one date format, and those that do not contain the string use another format. In other words, I want to distinguish between dataframes launched in year 2019 (which use mdy) and those launched in all others years (which use dmy).
The following code will conditionally mutate rows within a dataframe, but I am unsure how to conditionally mutate across the entire column.
dataframes %>% map(~.x %>%
mutate(date_time = if_else(str_detect(date_time, "/19 "),
mdy_hms(date_time), dmy_hms(date_time)))
Thank you!
edit
Data and code example. There are dataframes that contain a mixture of years.
library(tidyverse)
library(lubridate)
dataframes <- list(
tibble(date_time = c("07/06/19 01:00:00 PM", "07/06/20 01:00:00 PM"), num = 1:2), # July 6th
tibble(date_time = c("06/07/20 01:00:00 PM", "06/07/21 01:00:00 PM"), num = 1:2) # July 6th
)
dataframes %>%
map(~.x %>%
mutate(date_time = if_else(str_detect(date_time, "/19 "),
mdy_hms(date_time), dmy_hms(date_time)),
date = date(date_time),
month = month(date_time),
doy = yday(date_time)))
[[1]]
# A tibble: 2 × 5
date_time num date month doy
<dttm> <int> <date> <dbl> <dbl>
1 2019-07-06 13:00:00 1 2019-07-06 7 187
2 2020-06-07 13:00:00 2 2020-06-07 6 159
[[2]]
# A tibble: 2 × 5
date_time num date month doy
<dttm> <int> <date> <dbl> <dbl>
1 2020-07-06 13:00:00 1 2020-07-06 7 188
2 2021-07-06 13:00:00 2 2021-07-06 7 187

Answer 1

If you are trying to determine the format of the date column for the whole data.frame based on the presence of any date from 2019, then a small tweak of your code should work.
Instead of evaluating each record for the presence of /19 , you set the condition of the if_else() to be any(str_detect(...)) which returns TRUE if any of the values are TRUE. However the result of any() is always of length 1 so you then need to rep() the result to match the length of the whole data.frame using dplyr::n().
library(tidyverse)
library(lubridate)
dataframes <- list(
tibble(date_time = c("07/06/19 01:00:00 PM", "07/06/20 01:00:00 PM"), num = 1:2), # July 6th
tibble(date_time = c("06/07/20 01:00:00 PM", "06/07/21 01:00:00 PM"), num = 1:2) # July 6th
)
dataframes %>%
map( ~ .x %>%
mutate(
date_time = if_else(str_detect(date_time, "/19 ") %>%
any() %>%
rep(n()),
mdy_hms(date_time),
dmy_hms(date_time)),
date = date(date_time),
month = month(date_time),
doy = yday(date_time)
))
#> [[1]]
#> # A tibble: 2 × 5
#> date_time num date month doy
#> <dttm> <int> <date> <dbl> <dbl>
#> 1 2019-07-06 13:00:00 1 2019-07-06 7 187
#> 2 2020-07-06 13:00:00 2 2020-07-06 7 188
#>
#> [[2]]
#> # A tibble: 2 × 5
#> date_time num date month doy
#> <dttm> <int> <date> <dbl> <dbl>
#> 1 2020-07-06 13:00:00 1 2020-07-06 7 188
#> 2 2021-07-06 13:00:00 2 2021-07-06 7 187
Created on 2022-07-20 by the reprex package (v2.0.1)