[R] Extract year from date

Mark Sharp
Sun, 08 Mar 2015 20:45:08 -0000

Make the question reproducible (I used dput after getting the data into a
dataframe).
You need to provide a date of origin for the as.Date function.
Try lubridate package.

library(lubridate)
wells <- structure(list(ID = structure(c(3L, 3L, 2L, 1L, 3L, 2L, 3L, 1L,
 1L, 2L, 3L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L, 1L), .Label =
c("BC-0002",
 "BC-0003", "BC-0004"), class = "factor"), Date =
c(41163L, 41255L,
 41345L, 41351L, 41355L, 41438L, 41438L, 41443L, 41521L, 41522L,
 41522L, 41627L, 41627L, 41634L, 41703L, 41703L, 41710L, 41795L,
 41795L, 41801L, 41905L, 41905L, 41906L), DepthtoWater_bgs = c(260.6,
 261.65, 166.58, 317.85, 262.15, 167.55, 265.45, 317.25, 321.25,
 168.65, 266.15, 168.95, 265.25, 312.31, 169.25, 265.05, 313.01,
 168.85, 266.95, 330.41, 169.75, 267.75, 321.01), test = 3:25,
 test2 = 1:23), .Names = c("ID", "Date",
"DepthtoWater_bgs",
 "test", "test2"), class = "data.frame", row.names
= c("1", "2",
 "3", "4", "5", "6", "7",
"8", "9", "10", "11", "12",
"13", "14",
 "15", "16", "17", "18", "19",
"20", "21", "22", "23"))

wells$year <- year(as.Date(wells$Date, origin = '1900-1-1'))
head(wells$year)

Mark

R. Mark Sharp, Ph.D.
Director of Primate Records Database
Southwest National Primate Research Center
Texas Biomedical Research Institute
P.O. Box 760549
San Antonio, TX 78245-0549
Telephone: (210)258-9476
e-mail: msharp at TxBiomed.org



> On Mar 8, 2015, at 12:50 AM, Steve Archambault <archstevej at
gmail.com> wrote:
>
> Hi all,
>
> I am trying in vain to create a new object "Year" in my data
frame from
> existing Date data. I have tried many different approaches, but can't
seem
> to get it to work. Here is an example of some code I tried.
>
> date1<- as.Date(wells$Date,"%m/%d/%Y")
> wells$year<-as.numeric(format(date1, "%Y"))
>
> I am starting with data that looks like this.
>
>        ID  Date DepthtoWater_bgs test test2
> 1  BC-0004 41163           260.60    3     1
> 2  BC-0004 41255           261.65    4     2
> 3  BC-0003 41345           166.58    5     3
> 4  BC-0002 41351           317.85    6     4
> 5  BC-0004 41355           262.15    7     5
> 6  BC-0003 41438           167.55    8     6
> 7  BC-0004 41438           265.45    9     7
> 8  BC-0002 41443           317.25   10     8
> 9  BC-0002 41521           321.25   11     9
> 10 BC-0003 41522           168.65   12    10
> 11 BC-0004 41522           266.15   13    11
> 12 BC-0003 41627           168.95   14    12
> 13 BC-0004 41627           265.25   15    13
> 14 BC-0002 41634           312.31   16    14
> 15 BC-0003 41703           169.25   17    15
> 16 BC-0004 41703           265.05   18    16
> 17 BC-0002 41710           313.01   19    17
> 18 BC-0003 41795           168.85   20    18
> 19 BC-0004 41795           266.95   21    19
> 20 BC-0002 41801           330.41   22    20
> 21 BC-0003 41905           169.75   23    21
> 22 BC-0004 41905           267.75   24    22
> 23 BC-0002 41906           321.01   25    23
>
> Any help would be greatly appreciated!
>
> -Steve
> Sent from my iPhone
>
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