Join two data frames in R based on closest timestamp

Question

Hi I have two tables (table1 and table2 below) and would like to join them based on the closest timestamp to form expected_output. Some kind of solution involving dplyr wou

Answer 1

This is liable to be slow, but...

d   <- function(x,y) abs(x-y) # define the distance function
idx <- sapply( table1$date, function(x) which.min( d(x,table2$date) )) # find matches

cbind(table1,table2[idx,-1,drop=FALSE])
#                  date val1 val2
# 2 2015-07-16 08:55:00   94   90
# 3 2015-06-20 00:15:00   33   18
# 1 2015-05-12 15:00:00   53   67

Another way of constructing idx is max.col(-outer(table1$date, table2$date, d)).