I've got some data which is character class:
class(solarX[,MEASDATE])
[1] "character"
Which looks like :
head(solarX[,MEASDATE])
[1] "1/05/2015 0:00" "1/05/2015 0:30" "1/05/2015 1:00" "1/05/2015 1:30" "1/05/2015 2:00" "1/05/2015 2:30"
However, I don't want it in character format and need to be able to access the Hours and Minutes part of the date-time.
What i've tried is:
strptime(solarX[,MEASDATE], "%d/%m/%Y %H:%M"))
Which works great, it gives me:
[1] "2015-05-01 00:00:00 AEST" "2015-05-01 00:30:00 AEST" "2015-05-01 01:00:00 AEST" "2015-05-01 01:30:00 AEST" "2015-05-01 02:00:00 AEST"
[6] "2015-05-01 02:30:00 AEST"
class(strptime(solarX[,MEASDATE], "%d/%m/%Y %H:%M"))
[1] "POSIXlt" "POSIXt"
However, when I go to augment my original data table by doing:
solarX[, date := strptime(solarX[,MEASDATE], "%d/%m/%Y %H:%M")]
(solarX is my data table)
I get the following warning:
Warning message:
In `[.data.table`(solarX, , `:=`(date, strptime(solarX[, MEASDATE], :
Supplied 11 items to be assigned to 17568 items of column 'date' (recycled leaving remainder of 1 items)
And the data table returned looks terrible:
MEASDATE rrp exp_kwh date
1: 1/05/2015 0:00 33.99299 0 0,0,0,0,0,0,
2: 1/05/2015 0:30 31.53335 0 0,30, 0,30, 0,30,
3: 1/05/2015 1:00 29.37092 0 0,0,1,1,2,2,
4: 1/05/2015 1:30 28.03197 0 1,1,1,1,1,1,
5: 1/05/2015 2:00 26.82800 0 4,4,4,4,4,4,
6: 1/05/2015 2:30 25.22149 0 115,115,115,115,115,115,
Clearly I don't want the "date" column to look like that, rather have it filled with the values i got from the original strptime function.
You can't use POSIXlt in data.table, use POSIXct instead:
library(data.table)
## setting up the data
solarX <- fread('MEASDATE rrp exp_kwh
"1/05/2015 0:00" 33.99299 0
"1/05/2015 0:30" 31.53335 0
"1/05/2015 1:00" 29.37092 0
"1/05/2015 1:30" 28.03197 0
"1/05/2015 2:00" 26.82800 0
"1/05/2015 2:30" 25.22149 0')
solarX[, date := as.POSIXct(MEASDATE, format = "%d/%m/%Y %H:%M")]
# MEASDATE rrp exp_kwh date
# 1: 1/05/2015 0:00 33.99299 0 2015-05-01 00:00:00
# 2: 1/05/2015 0:30 31.53335 0 2015-05-01 00:30:00
# 3: 1/05/2015 1:00 29.37092 0 2015-05-01 01:00:00
# 4: 1/05/2015 1:30 28.03197 0 2015-05-01 01:30:00
# 5: 1/05/2015 2:00 26.82800 0 2015-05-01 02:00:00
# 6: 1/05/2015 2:30 25.22149 0 2015-05-01 02:30:00
str(solarX)
Classes ‘data.table’ and 'data.frame': 6 obs. of 4 variables:
$ MEASDATE: chr "1/05/2015 0:00" "1/05/2015 0:30" "1/05/2015 1:00" "1/05/2015 1:30" ...
$ rrp : num 34 31.5 29.4 28 26.8 ...
$ exp_kwh: int 0 0 0 0 0 0
$ date : POSIXct, format: "2015-05-01 00:00:00" "2015-05-01 00:30:00" "2015-05-01 01:00:00" "2015-05-01 01:30:00" ...
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