Merge multiple xts objects with matching or nearest dates

Question

I have two xts files with daily data (The data is only one date for a month). The first file is this: - The dates in this xts are typically end of the month trading dates in a given month.

structure(c(-0.0329199999999997, 0.0874901766141374, 0.0545883292605231, 
            0.0687945180777207, 0.0550784545301166, 0.074678777314922, -0.0866534235058661, 
            0.161206236457536, 0.0704023794825748, 0.074691325661258), class = c("xts",
                                                                                 "zoo"), ret_type = "discrete", coredata_content = "discreteReturn", index = structure(c(1114732800, 
                                                                                                                                                                         1117497600, 1120089600, 1122595200, 1125446400, 1128038400, 1130716800, 
                                                                                                                                                                         1133308800, 1135900800, 1138665600), tzone = "UTC", tclass = "Date"), dim = c(10L, 
                                                                                                                                                                                                                                                       1L), dimnames = list(NULL, "xts_left"))

The second xts file is:

structure(c(0.0052512320343876, 0.00540733325225928, 0.00580017750416384, 
            0.005701283061746, 0.00556285472234541, 0.00561113650865441, 
            0.00580424365658105, 0.005816988308881, 0.00571552920344676, 
            0.00574088497469671, 0.00574737930337577, 0.00589584054618375, 
            0.00592325487612455), class = c("xts", "zoo"), .CLASS = "double", index = structure(c(1107216000, 
                                                                                                  1109635200, 1112313600, 1114905600, 1117584000, 1120176000, 1122854400, 
                                                                                                  1125532800, 1128124800, 1130803200, 1133395200, 1136073600, 1138752000
            ), tzone = "UTC", tclass = "Date"), dim = c(13L, 1L))

This is how I want the output of the merge: To pick the value from right xts that corresponds to the closest date value in the left xts. For example, the value on 29-04-2005 be matched with the nearest, ie 01-05-2005 (dd-mm-yyyy format).

I have seen a possible way to do this using data.table with rolling joins, but I wanted to know if there is a way to do this within the xts (or similar) framework.

Answer 1

Using x1 and x2 in the Note at the end define near which given a date, tt, finds the nearest date in x2 and returns the corresponding data value. Then apply that to each date in x1.

near <- function(tt) x2[which.min(abs(time(x2) - tt))]
x12 <- transform(x1, xts_right = sapply(time(x1), near)); x12

giving:

              xts_left   xts_right
2005-04-29 -0.03292000 0.005701283
2005-05-31  0.08749018 0.005562855
2005-06-30  0.05458833 0.005611137
2005-07-29  0.06879452 0.005804244
2005-08-31  0.05507845 0.005816988
2005-09-30  0.07467878 0.005715529
2005-10-31 -0.08665342 0.005740885
2005-11-30  0.16120624 0.005747379
2005-12-30  0.07040238 0.005895841
2006-01-31  0.07469133 0.005923255

Note

x1 <-
structure(c(-0.0329199999999997, 0.0874901766141374, 0.0545883292605231, 
0.0687945180777207, 0.0550784545301166, 0.074678777314922, -0.0866534235058661, 
0.161206236457536, 0.0704023794825748, 0.074691325661258), .Dim = c(10L, 
1L), class = c("xts", "zoo"), ret_type = "discrete", 
coredata_content = "discreteReturn", index = structure(c(1114732800, 
1117497600, 1120089600, 1122595200, 1125446400, 1128038400, 1130716800, 
1133308800, 1135900800, 1138665600), tzone = "UTC", tclass = "Date"), 
.Dimnames = list(NULL, "xts_left"))

x2 <-
structure(c(0.0052512320343876, 0.00540733325225928, 0.00580017750416384, 
0.005701283061746, 0.00556285472234541, 0.00561113650865441, 
0.00580424365658105, 0.005816988308881, 0.00571552920344676, 
0.00574088497469671, 0.00574737930337577, 0.00589584054618375, 
0.00592325487612455), .Dim = c(13L, 1L), class = c("xts", "zoo"
), .CLASS = "double", index = structure(c(1107216000, 1109635200, 
1112313600, 1114905600, 1117584000, 1120176000, 1122854400, 1125532800, 
1128124800, 1130803200, 1133395200, 1136073600, 1138752000), 
tzone = "UTC", tclass = "Date"))