How do I group my date variable into month/year in R?
I have a "date" vector, that contains dates in mm/dd/yyyy format:
head(Entered_Date,5)
[1] 1/5/1998 1/5/1998 1/5/1998 1/5/1998 1/5/1998
I am trying to plot a frequency variable against the date, but I want to group the dates that it is by month or year. As it is now, there is a frequency per day, but I want to plot the frequency by month or year. So instead of having a frequency of 1 for 1/5/1998, 1 for 1/7/1998, and 3 for 1/8/1998, I would like to display it as 5 for 1/1998. It is a relatively large data set, with dates from 1998 to present, and I would like to find some automated way to accomplish this.
> dput(head(Entered_Date))
structure(c(260L, 260L, 260L, 260L, 260L, 260L), .Label = c("1/1/1998",
"1/1/1999", "1/1/2001", "1/1/2002", "1/10/2000", "1/10/2001",
"1/10/2002", "1/10/2003", "1/10/2005", "1/10/2006", "1/10/2007",
"1/10/2008", "1/10/2011", "1/10/2012", "1/10/2013", "1/11/1999",
"1/11/2000", "1/11/2001", "1/11/2002", "1/11/2005", "1/11/2006",
"1/11/2008", "1/11/2010", "1/11/2011", "1/11/2012", "1/11/2013",
"1/12/1998", "1/12/1999", "1/12/2001", "1/12/2004", "1/12/2005", ...
Answer
Here is an example using dplyr. You simply use the corresponding date format string for month %m or year %Y in the format statement.
set.seed(123)
df <- data.frame(date = seq.Date(from =as.Date("01/01/1998", "%d/%m/%Y"),
to=as.Date("01/01/2000", "%d/%m/%Y"), by="day"),
value = sample(seq(5), 731, replace = TRUE))
head(df)
date value
1 1998-01-01 2
2 1998-01-02 4
3 1998-01-03 3
4 1998-01-04 5
5 1998-01-05 5
6 1998-01-06 1
library(dplyr)
df %>%
mutate(month = format(date, "%m"), year = format(date, "%Y")) %>%
group_by(month, year) %>%
summarise(total = sum(value))
Source: local data frame [25 x 3]
Groups: month [?]
month year total
(chr) (chr) (int)
1 01 1998 105
2 01 1999 91
3 01 2000 3
4 02 1998 74
5 02 1999 77
6 03 1998 96
7 03 1999 86
8 04 1998 91
9 04 1999 95
10 05 1998 93
.. ... ... ...