R - Assign column value based on closest match in second data frame

Question

I have two data frames, logger and df (times are numeric):

logger <- data.frame(
time = c(1280248354:1280248413),
temp = runif(60,min=18,max=24.5)
)

df &         


        

Answer 1

You could use the data.table library. This will also help with being more efficient with large data size -

library(data.table)

logger <- data.frame(
  time = c(1280248354:1280248413),
  temp = runif(60,min=18,max=24.5)
)

df <- data.frame(
  obs = c(1:10),
  time = runif(10,min=1280248354,max=1280248413)
)

logger <- data.table(logger)
df <- data.table(df)

setkey(df,time)
setkey(logger,time)

df2 <- logger[df, roll = "nearest"]

Output -

> df2
          time     temp obs
 1: 1280248356 22.81437   7
 2: 1280248360 24.08711  10
 3: 1280248366 22.31738   2
 4: 1280248367 18.61222   5
 5: 1280248388 19.46300   4
 6: 1280248393 18.26535   6
 7: 1280248400 20.61901   9
 8: 1280248402 21.92584   1
 9: 1280248410 19.36526   8
10: 1280248410 19.36526   3