I have data frame in R, where two columns are datetimes (POSIX class). I need to calculate mean datetime by each row.
Here's some reproducible example:
a <- c(
"2018-10-11 15:22:17",
"2018-10-10 16:30:37",
"2018-10-10 16:52:46",
"2018-10-10 16:58:33",
"2018-10-10 16:32:24")
b <- c(
"2018-10-11 15:25:12",
"2018-10-10 16:30:39",
"2018-10-10 16:55:14",
"2018-10-10 16:58:53",
"2018-10-10 16:32:27")
a <- strptime(a, format = "%Y-%m-%d %H:%M:%S")
b <- strptime(b, format = "%Y-%m-%d %H:%M:%S")
f <- data.frame(a, b)
The results should be like that:
a b time_mean
1 2018-10-11 15:22:17 2018-10-11 15:25:12 2018-10-11 15:23:44
2 2018-10-10 16:30:37 2018-10-10 16:30:39 2018-10-10 16:30:38
3 2018-10-10 16:52:46 2018-10-10 16:55:14 2018-10-10 16:54:00
4 2018-10-10 16:58:33 2018-10-10 16:58:53 2018-10-10 16:58:43
5 2018-10-10 16:32:24 2018-10-10 16:32:27 2018-10-10 16:32:25
I tried following:
apply(f, 1, function(x) mean)
apply(f, 1, function(x) mean(c(x[1], x[2])))
Instead of using apply (which can convert it to a matrix and then strip off the class attributes), use Map
f$time_mean <- do.call(c, Map(function(x, y) mean(c(x, y)), a, b))
f$time_mean
#[1] "2018-10-11 15:23:44 EDT" "2018-10-10 16:30:38 EDT" "2018-10-10 16:54:00 EDT" "2018-10-10 16:58:43 EDT"
#[5] "2018-10-10 16:32:25 EDT"
Or as it is from data.frame f
do.call(c, Map(function(x, y) mean(c(x, y)), f$a, f$b))
Also, another option is converting to numeric class with ?xtfrm (that also has POSIXlt method dispatch), do the rowMeans and convert to DateTime class as in @jay.sf's post
as.POSIXlt(rowMeans(sapply(f, xtfrm)), origin = "1970-01-01")
#[1] "2018-10-11 15:23:44 EDT" "2018-10-10 16:30:38 EDT" "2018-10-10 16:54:00 EDT" "2018-10-10 16:58:43 EDT"
#[5] "2018-10-10 16:32:25 EDT"
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