How to Aggregate Daily Data to Monthly and Yearly in R


Occasionally you may want to aggregate daily data to weekly, monthly, or yearly data in R.

This tutorial explains how to easily do so using the lubridate and dplyr packages.

Example: Aggregate Daily Data in R

Suppose we have the following data frame in R that shows the daily sales of some item over the course of 100 consecutive days:

#make this example reproducible
set.seed(1)

#create data frame 
df <- data.frame(date = as.Date("2020-12-01") + 0:99,
                 sales = runif(100, 20, 50))

#view first six rows
head(df)

        date    sales
1 2020-12-01 27.96526
2 2020-12-02 31.16372
3 2020-12-03 37.18560
4 2020-12-04 47.24623
5 2020-12-05 26.05046
6 2020-12-06 46.95169

To aggregate this data, we can use the floor_date() function from the lubridate package which uses the following syntax:

floor_date(x, unit)

where:

  • x: A vector of date objects.
  • unit: A time unit to round to. Options include second, minute, hour, day, week, month, bimonth, quarter, halfyear, and year.

The following code snippets show how to use this function along with the group_by() and summarize() functions from the dplyr package to find the mean sales by week, month, and year:

Mean Sales by Week

library(lubridate)
library(dplyr)

#round dates down to week
df$week <- floor_date(df$date, "week")

#find mean sales by week
df %>%
  group_by(week) %>%
  summarize(mean = mean(sales))

# A tibble: 15 x 2
   week        mean
        
 1 2020-11-29  33.9
 2 2020-12-06  35.3
 3 2020-12-13  39.0
 4 2020-12-20  34.4
 5 2020-12-27  33.6
 6 2021-01-03  35.9
 7 2021-01-10  37.8
 8 2021-01-17  36.8
 9 2021-01-24  32.8
10 2021-01-31  33.9
11 2021-02-07  34.1
12 2021-02-14  41.6
13 2021-02-21  31.8
14 2021-02-28  35.2
15 2021-03-07  37.1

Mean Sales by Month

library(lubridate)
library(dplyr)

#round dates down to week
df$month <- floor_date(df$date, "month")

#find mean sales by month
df %>%
  group_by(month) %>%
  summarize(mean = mean(sales))

# A tibble: 4 x 2
  month       mean
       
1 2020-12-01  35.3
2 2021-01-01  35.6
3 2021-02-01  35.2
4 2021-03-01  37.0

Mean Sales by Year

library(lubridate)
library(dplyr)

#round dates down to week
df$year <- floor_date(df$date, "year")

#find mean sales by month
df %>%
  group_by(year) %>%
  summarize(mean = mean(sales))

# A tibble: 2 x 2
  year        mean
       
1 2020-01-01  35.3
2 2021-01-01  35.7

Note that we chose to aggregate by the mean, but we could use any summary statistic we’d like such as the median, mode, max, min, etc.

Additional Resources

How to Calculate the Mean by Group in R
How to Calculate Cumulative Sums in R
How to Plot a Time Series in R

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