tsibble

The tsibble package provides a data infrastructure for tidy temporal data with wrangling tools. Adapting the tidy data principles, tsibble is a data- and model-oriented object. In tsibble:

1. Index is a variable with inherent ordering from past to present.
2. Key is a set of variables that define observational units over time.
3. Each observation should be uniquely identified by index and key.
4. Each observational unit should be measured at a common interval, if regularly spaced.

Installation

You could install the stable version on CRAN:

install.packages("tsibble")

You could install the development version from Github using

# install.packages("remotes")
remotes::install_github("tidyverts/tsibble")

Get started

Coerce to a tsibble with as_tsibble()

To coerce a data frame to tsibble, we need to declare key and index. For example, in the weather data from the package nycflights13, the time_hour containing the date-times should be declared as index, and the origin as key. Other columns can be considered as measured variables.

library(dplyr)
library(tsibble)
weather <- nycflights13::weather %>% 
  select(origin, time_hour, temp, humid, precip)
weather_tsbl <- as_tsibble(weather, key = origin, index = time_hour)
weather_tsbl
#> # A tsibble: 26,115 x 5 [1h] <America/New_York>
#> # Key:       origin [3]
#>   origin time_hour            temp humid precip
#>   <chr>  <dttm>              <dbl> <dbl>  <dbl>
#> 1 EWR    2013-01-01 01:00:00  39.0  59.4      0
#> 2 EWR    2013-01-01 02:00:00  39.0  61.6      0
#> 3 EWR    2013-01-01 03:00:00  39.0  64.4      0
#> 4 EWR    2013-01-01 04:00:00  39.9  62.2      0
#> 5 EWR    2013-01-01 05:00:00  39.0  64.4      0
#> # … with 2.611e+04 more rows

The key can be comprised of empty, one, or more variables. See package?tsibble and vignette("intro-tsibble") for details.

The interval is computed from index based on the representation, ranging from year to nanosecond, from numerics to ordered factors. The table below shows how tsibble interprets the common time formats.

fill_gaps() to turn implicit missing values into explicit missing values

Often there are implicit missing cases in time series. If the observations are made at regular time interval, we could turn these implicit missingness to be explicit simply using fill_gaps(), filling gaps in precipitation (precip) with 0 in the meanwhile. It is quite common to replaces NAs with its previous observation for each origin in time series analysis, which is easily done using fill() from tidyr.

full_weather <- weather_tsbl %>%
  fill_gaps(precip = 0) %>% 
  group_by_key() %>% 
  tidyr::fill(temp, humid, .direction = "down")
full_weather
#> # A tsibble: 26,190 x 5 [1h] <America/New_York>
#> # Key:       origin [3]
#> # Groups:    origin [3]
#>   origin time_hour            temp humid precip
#>   <chr>  <dttm>              <dbl> <dbl>  <dbl>
#> 1 EWR    2013-01-01 01:00:00  39.0  59.4      0
#> 2 EWR    2013-01-01 02:00:00  39.0  61.6      0
#> 3 EWR    2013-01-01 03:00:00  39.0  64.4      0
#> 4 EWR    2013-01-01 04:00:00  39.9  62.2      0
#> 5 EWR    2013-01-01 05:00:00  39.0  64.4      0
#> # … with 2.618e+04 more rows

fill_gaps() also handles filling in time gaps by values or functions, and respects time zones for date-times. Wanna a quick overview of implicit missing values? Check out vignette("implicit-na").

index_by() + summarise() to aggregate over calendar periods

index_by() is the counterpart of group_by() in temporal context, but it groups the index only. In conjunction with index_by(), summarise() and its scoped variants aggregate interested variables over calendar periods. index_by() goes hand in hand with the index functions including as.Date(), yearweek(), yearmonth(), and yearquarter(), as well as other friends from lubridate. For example, it would be of interest in computing average temperature and total precipitation per month, by applying yearmonth() to the index variable (referred to as .).

full_weather %>%
  group_by_key() %>%
  index_by(year_month = ~ yearmonth(.)) %>% # monthly aggregates
  summarise(
    avg_temp = mean(temp, na.rm = TRUE),
    ttl_precip = sum(precip, na.rm = TRUE)
  )
#> # A tsibble: 36 x 4 [1M]
#> # Key:       origin [3]
#>   origin year_month avg_temp ttl_precip
#>   <chr>       <mth>    <dbl>      <dbl>
#> 1 EWR      2013 Jan     35.6       3.53
#> 2 EWR      2013 Feb     34.2       3.83
#> 3 EWR      2013 Mar     40.1       3   
#> 4 EWR      2013 Apr     53.0       1.47
#> 5 EWR      2013 May     63.3       5.44
#> # … with 31 more rows

While collapsing rows (like summarise()), group_by() and index_by() will take care of updating the key and index respectively. This index_by() + summarise() combo can help with regularising a tsibble of irregular time space too.

Rolling with functional programming: slide(), tile(), stretch()

Temporal data often involves moving window calculations. Several functions in tsibble allow for different variations of moving windows using purrr-like syntax:

• slide()/slide2()/pslide(): sliding window with overlapping observations.
• tile()/tile2()/ptile(): tiling window without overlapping observations.
• stretch()/stretch2()/pstretch(): fixing an initial window and expanding to include more observations.

For example, a moving average of window size 3 is carried out on hourly temperatures for each group (origin).

full_weather %>% 
  group_by_key() %>% 
  mutate(temp_ma = slide_dbl(temp, ~ mean(., na.rm = TRUE), .size = 3))
#> # A tsibble: 26,190 x 6 [1h] <America/New_York>
#> # Key:       origin [3]
#> # Groups:    origin [3]
#>   origin time_hour            temp humid precip temp_ma
#>   <chr>  <dttm>              <dbl> <dbl>  <dbl>   <dbl>
#> 1 EWR    2013-01-01 01:00:00  39.0  59.4      0    NA  
#> 2 EWR    2013-01-01 02:00:00  39.0  61.6      0    NA  
#> 3 EWR    2013-01-01 03:00:00  39.0  64.4      0    39.0
#> 4 EWR    2013-01-01 04:00:00  39.9  62.2      0    39.3
#> 5 EWR    2013-01-01 05:00:00  39.0  64.4      0    39.3
#> # … with 2.618e+04 more rows

Looking for rolling in parallel? Their multiprocessing equivalents are prefixed with future_. More examples can be found at vignette("window").

Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms.