how to find dates that overlap from two different dataframes and subset

Question

I would like to use a date from dataframe A to find any dates within 180 days of this date to select rows in dataframe B, with matching ID\'s.

eg.

Answer 1

If you have a big data, I would suggest using data.tables rolling join instead

Assuming these are your data sets

dfa <- read.table(text = "ID  Date
                  42  '2012-07-21'
                  42  '2013-04-12'", header = TRUE)

dfb <- read.table(text = "ID Date
                  12 '2016-09-08'
                  35 '2008-02-02'
                  42 '2012-01-09'
                  42 '2013-03-13'", header = TRUE)

We will convert them to data.tables and convert the Date column to IDate class

library(data.table) #1.9.8+
setDT(dfa)[, Date := as.IDate(Date)]
setDT(dfb)[, Date := as.IDate(Date)]

Then, simply join away (you can do the rolling join both ways)

# You can perform another rolling join for `roll = -180` too
indx <- dfb[
            dfa, # Per each row in dfa find a match in dfb
            on = .(ID, Date), # The columns to join by
            roll = 180, # Rolling window, can join again on -180 afterwards
            which = TRUE, # Return the row index within `dfb` that been matched
            mult = "first", # Multiple match handling- take only the first match
            nomatch = 0L # Don't return unmatched indexes (NAs)
           ]

dfb[indx]
#    ID       Date
# 1: 42 2013-03-13

---

An alternative way achieving this, is to use data.tables non-equi join feature on Date +-180 (manually created) columns

# Create range columns
dfa[, c("Date_m_180", "Date_p_180") := .(Date - 180L, Date + 180L)]

# Join away
indx <- dfb[dfa, 
            on = .(ID, Date >= Date_m_180, Date <= Date_p_180), 
            which = TRUE, 
            mult = "first",
            nomatch = 0L]
dfb[indx]
#    ID       Date
# 1: 42 2013-03-13

Both methods should handle large data sets almost instantly