R-- Return value with the nearest date [duplicate]

Question

I am attempting to extract the closest value based on date between 2 tables.

Table 1 looks like:

id	value	date
1	aa	10/2/21
2	ab	4/6/18

Table 2 looks like:

id	value_2	date_2
1	ba	4/12/11
1	bb	8/16/08
1	bc	10/4/21
2	bd	4/26/18
2	bd	3/26/19

I would like the output table to return value_2 that corresponds to the same id in both tables based on the closest date. ex- id 1 should return value bc since 10/4/21 is closest to 10/2/21

So the output table should mutate this value_2 to look like-

id	value	date	value_2
1	aa	10/2/21	bc
2	ab	4/6/18	bd

Answer 1

There's currently an error in one of the date formats. Further there's some unclarity on what is "closest" (do we only look back or do we also look forward?)

If we are only interested in truly "closest", we could simply use a k-nearest neighbour approach with a single neighbour (k = 1).

library(e1071)
table1 <- data.frame(value = factor(c('aa', 'ab')), 
                     date = as.Date(c('10/2/21', '4/6/18'), 
                                    tryFormats = c('%m/%d/%y', '%d/%m/%y')))
table2 <- data.frame(value = factor(c('ba', 'bb', 'bc', 'bd', 'bd')),
                     date = as.Date(c('4/12/11', '8/16/08', 
                                      # Chagned for example
                                      '2/15/21', 
                                      '4/26/18', '3/26/19'),
                                    tryFormats = c('%m/%d/%y', '%d/%m/%y')))
mod <- gknn(value ~ date, k = 1, data = table2)
table1$predict <- predict(mod, newdata = table1)
table1
#        value       date predict
#      1    aa 2021-10-02      bc
#      2    ab 2018-04-06      bd