r - Apply + lubridate returns numeric -

i have data set looks

birds[,1:3] source: local data frame [15 x 3]     year month day 1  2015     5  13 2  2015     5  14 3  2015     5  15 4  2015     5  16 5  2015     5  17 6  2014     5  28 7  2014     5  29 8  2014     5  30 9  2014     5  31 10 2014     6   1 11 2013     5   8 12 2013     5   9 13 2013     5  10 14 2013     5  11 15 2013     5  12 

what combine these columns 1 "date" column, figured paste them , pass them lubridate.

this works:

ymd(paste(birds[1,1], birds[1,2], birds[1,3], sep="-")) [1] "2015-05-13 utc" 

but when try use apply every row this:

apply(birds[,c("year","month","day")], 1,  function(x) ymd(paste(x[1], x[2], x[3], sep="-")))  [1] 1431475200 1431561600 1431648000 1431734400 1431820800 1401235200 1401321600 1401408000 1401494400  [10] 1401580800 1367971200 1368057600 1368144000 1368230400 1368316800 

why happen , how fix it?

we don't need apply margin=1. instead, can paste columns with(birds, paste(year, month, day, sep="-")) , wrap as.date convert 'date' class. output of ymd posixct class, within apply, coerced 'numeric' form.

library(lubridate) library(dplyr) mutate(birds, date=ymd(paste(year, month, day))) 

or can use unite tidyr , convert posixct class

library(tidyr) unite(birds, date, year:day, sep="-") %>%             mutate(date=ymd(date)) 

or using do.call base r ymd

birds$date <- ymd(do.call(paste, birds)) 

or can use as.date base r

as.date(do.call(paste, c(birds,sep="-"))) 

to fix output obtained apply

res <- apply(birds[,c("year","month","day")], 1,        function(x) ymd(paste(x[1], x[2], x[3], sep="-"))) unname(as.posixct(res, origin='1970-01-01',tz='utc')) #[1] "2015-05-13 utc" "2015-05-14 utc" "2015-05-15 utc" "2015-05-16 utc" #[5] "2015-05-17 utc" "2014-05-28 utc" "2014-05-29 utc" "2014-05-30 utc" #[9] "2014-05-31 utc" "2014-06-01 utc" "2013-05-08 utc" "2013-05-09 utc" #[13] "2013-05-10 utc" "2013-05-11 utc" "2013-05-12 utc" 

data

birds <- structure(list(year = c(2015l, 2015l, 2015l, 2015l, 2015l,  2014l,  2014l, 2014l, 2014l, 2014l, 2013l, 2013l, 2013l, 2013l, 2013l ), month = c(5l, 5l, 5l, 5l, 5l, 5l, 5l, 5l, 5l, 6l, 5l, 5l,  5l, 5l, 5l), day = c(13l, 14l, 15l, 16l, 17l, 28l, 29l, 30l,  31l, 1l, 8l, 9l, 10l, 11l, 12l)), .names = c("year", "month",  "day"), class = "data.frame", row.names = c("1", "2", "3", "4",  "5", "6", "7", "8", "9", "10", "11", "12", "13", "14", "15"))