How to run left join in dplyr transforming the key columns ( using lubridate function) on the fly

Question

I have two databases where I need to combine columns based on 2 common Date columns, with condition that the DAY for those dates are the same.

"2020/01/01 20:30" MUST MATCH "2020/01//01 17:50"

All dates are in POSIXct format. While I could use some pre-cprocessing with string parsing or the like, I wanted to handle it via lubridate/dplyr like:

DB_New <- left_join(DB_A,DB_B, by=c((date(Date1) = date(Date2)))

notice I am using the function "date" from dplyr to rightly match condition as explained above. I am though getting the error as below:

DB_with_rain <- left_join(DB_FEB_2019_join,Chuvas_BH, by=c(date(Saida_Real)= date(DateTime))) Error: unexpected '=' in "DB_with_rain <- left_join(DB_FEB_2019_join,Chuvas_BH, by=c(date(Saida_Real)="

Answer 1

Within in the by, we cannot do the conversion - it expects the column name as a string. It should be done before the left_join

library(dplyr)
DF_FEB_2019_join %>%
    mutate(Saida_Real = as.Date(Saida_Real, format = "%Y/%m/%d %H:%M")) %>%
    left_join(Chuvas_BH %>%
            mutate(DateTime = as.Date(DateTime, format = "%Y/%m/%d %H:%M")),
        by = c(Saida_Real = "DateTime"))

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With lubridate function, the as.Date can be replaced with ymd_hm and convert to Date class with as.Date