R chron %in% comparison only recognizes every second date

Question

I am using zoo and chron packages in R to read and transform data. At one point I need to select a part of a chron-indexed zoo object which corresponds to another chron object. Unfortunately, using %in% operator I only get part of the corresponding dates. Here is a MWE that reproduces the error:

library(chron)
library(zoo)
chron1 <- seq(chron("2013-01-01","00:00:00", format=c(dates="y-m-d",times="h:m:s")),
              chron("2013-01-01","03:10:00", format=c(dates="y-m-d",times="h:m:s")),by=1./1440.)
x1 <- runif(200)
z1 <- zoo(x1,chron1)
chron10 <- trunc(chron1, "00:10:00")
x10 <- aggregate(z1,chron10,FUN=sum)
which(index(x10) %in% chron1)

The (unexpected) output is:

[1]  1  3  5  7  9 10 12 14 16 18 19

It's not `chron1a`, it's `chron1`. Please edit the question. — Rui Barradas, Mar 02 '18 at 13:35
This is a round off error issue, `index(x10)[1] - chron1[11]` outputs `[1] -0.006944444`. The following seems to solve it: `round(index(x10)) %in% round(chron1)`. — Rui Barradas, Mar 02 '18 at 13:38
@RuiBarradas: Thanks, edited the question. 'round' unfortunately rounds to full days. Not sure it works for minutes. — NicoH, Mar 02 '18 at 13:57

G. Grothendieck · Accepted Answer · 2018-03-02T14:15:34.323

chron objects are floating point so there can be slight differences in what appears to be the same datetime depending on how they were calculated. format them and compare those:

which(format(index(x10)) %in% format(chron1))
## [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20

This also works as trunc uses an eps value to ensure that inputs slightly less than one minute are not truncated down a further minute. See ?trunc.times

which(trunc(index(x10), "minutes") %in% trunc(chron1, "minutes"))
##  [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20

Also see R FAQ 7.31

R chron %in% comparison only recognizes every second date

1 Answers1