Monthly and quarterly data

Manipulating Time Series Data in R

Harrison Brown

Graduate Researcher in Geography

Dates and aggregated data

Dates:

ISO 8601
Largest -> smallest
2012-09-25

Aggregation:

Monthly mean
Weekly maximum
Daily median
Shows general trend and patterns in the data

Monthly data:

Which date to use?
Data for January, 2003:
- 2003-01-01?
- 2003-01-31?
- 2003-01-15?
- 2003-01

Year-month

Monthly data:

laborday_2022 <- as_date('2022-09-05')
laborday_2021 <- as_date('2021-09-06')

lubridate::month(laborday_2022)

[1] 9

lubridate::month(laborday_2021)

[1] 9

zoo::yearmon class:

year-month data

as.yearmon(laborday_2022)

[1] "Sep 2022"

as.yearmon(laborday_2021)

[1] "Sep 2021"

zoo::yearmon

zoo::as.yearmon()

as.yearmon('2007-10-31')

[1] "Oct 2007"

laborday_2021 <- as_date('2022-09-06')
as.yearmon(laborday_2022)

[1] "Sep 2021"

lunchtime <-
  as.POSIXct('2022-09-21 13:30:00 EDT')
as.yearmon(lunchtime)

[1] "Sep 2022"

as.yearmon(2008.245)

[1] "Mar 2008"

Monthly data

Time series plot of the "monthly sales" dataset - a fictional dataset of sales data aggregated to each month. The plot shows an upwards trend, and there is a seasonal peak at the beginning of each year.

class(index(monthly_sales))

[1] "yearmon"

monthly_sales

Jan 1990 209.8921
Feb 1990 209.1493
Mar 1990 214.5236
Apr 1990 206.0842
May 1990 202.5655
...

zoo::yearqtr

zoo::yearqtr class

as.yearqtr(2018.639)

[1] "2018 Q3"

eid_2022 <- as_date('2022-05-01')
as.yearqtr(eid_2022)

[1] "2022 Q2"

april_2003 <- as.yearmon("Apr 2003")
as.yearqtr(april_2003)

[1] "2003 Q2"

zoo::as.yearqtr('1990-10-30')

[1] NA

Quarterly data

Time series plot of the "quarterly sales" dataset - a fictional dataset of sales data aggregated to each quarter. The plot shows an upwards trend, and there is a seasonal peak at the beginning of each year.

quarterly_sales

1990 Q1 625.3594
1990 Q2 610.4269
1990 Q3 607.1768
1990 Q4 628.9146
1991 Q1 635.5531
...

class(index(quarterly_sales))

[1] "yearqtr"

Let's practice!

Manipulating Time Series Data in R