Create a tsibble object

Usage

tsibble(..., key = NULL, index, regular = TRUE, .drop = TRUE)

Arguments

...: A set of name-value pairs.
key: Variable(s) that uniquely determine time indices. NULL for empty key, and c() for multiple variables. It works with tidy selector (e.g. dplyr::starts_with()).
index: A variable to specify the time index variable.
regular: Regular time interval (TRUE) or irregular (FALSE). The interval is determined by the greatest common divisor of index column, if TRUE.
.drop: If TRUE, empty key groups are dropped.

Value

A tsibble object.

Details

A tsibble is sorted by its key first and index.

Index

An extensive range of indices are supported by tsibble:

native time classes in R (such as Date, POSIXct, and difftime)
tsibble's new additions (such as yearweek, yearmonth, and yearquarter).
other commonly-used classes: ordered, hms::hms, lubridate::period, and nanotime::nanotime.

For a tbl_ts of regular interval, a choice of index representation has to be made. For example, a monthly data should correspond to time index created by yearmonth, instead of Date or POSIXct. Because months in a year ensures the regularity, 12 months every year. However, if using Date, a month containing days ranges from 28 to 31 days, which results in irregular time space. This is also applicable to year-week and year-quarter.

Tsibble supports arbitrary index classes, as long as they can be ordered from past to future. To support a custom class, you need to define index_valid() for the class and calculate the interval through interval_pull().

Key

Key variable(s) together with the index uniquely identifies each record:

Empty: an implicit variable. NULL resulting in a univariate time series.
A single variable: For example, data(pedestrian) uses Sensor as the key.
Multiple variables: For example, Declare key = c(Region, State, Purpose) for data(tourism). Key can be created in conjunction with tidy selectors like starts_with().

Interval

The interval function returns the interval associated with the tsibble.

Regular: the value and its time unit including "nanosecond", "microsecond", "millisecond", "second", "minute", "hour", "day", "week", "month", "quarter", "year". An unrecognisable time interval is labelled as "unit".
Irregular: as_tsibble(regular = FALSE) gives the irregular tsibble. It is marked with !.
Unknown: Not determined (?), if it's an empty tsibble, or one entry for each key variable.

An interval is obtained based on the corresponding index representation:

integerish numerics between 1582 and 2499: "year" (Y). Note the year of 1582 saw the beginning of the Gregorian Calendar switch.
yearquarter: "quarter" (Q)
yearmonth: "month" (M)
yearweek: "week" (W)
Date: "day" (D)
difftime: "week" (W), "day" (D), "hour" (h), "minute" (m), "second" (s)
POSIXt/hms: "hour" (h), "minute" (m), "second" (s), "millisecond" (us), "microsecond" (ms)
period: "year" (Y), "month" (M), "day" (D), "hour" (h), "minute" (m), "second" (s), "millisecond" (us), "microsecond" (ms)
nanotime: "nanosecond" (ns)
other numerics &ordered (ordered factor): "unit" When the interval cannot be obtained due to the mismatched index format, an error is issued.

The interval is invariant to subsetting, such as filter(), slice(), and [.tbl_ts. However, if the result is an empty tsibble, the interval is always unknown. When joining a tsibble with other data sources and aggregating to different time scales, the interval gets re-calculated.

Examples

# create a tsibble w/o a key
tsibble(
  date = as.Date("2017-01-01") + 0:9,
  value = rnorm(10)
)
#> Using `date` as index variable.
#> # A tsibble: 10 x 2 [1D]
#>    date         value
#>    <date>       <dbl>
#>  1 2017-01-01  0.593 
#>  2 2017-01-02 -0.0653
#>  3 2017-01-03 -0.701 
#>  4 2017-01-04 -0.529 
#>  5 2017-01-05  0.170 
#>  6 2017-01-06  0.114 
#>  7 2017-01-07 -0.796 
#>  8 2017-01-08 -0.236 
#>  9 2017-01-09  1.19  
#> 10 2017-01-10  0.188 

# create a tsibble with a single variable for key
tsibble(
  qtr = rep(yearquarter("2010 Q1") + 0:9, 3),
  group = rep(c("x", "y", "z"), each = 10),
  value = rnorm(30),
  key = group
)
#> Using `qtr` as index variable.
#> # A tsibble: 30 x 3 [1Q]
#> # Key:       group [3]
#>        qtr group   value
#>      <qtr> <chr>   <dbl>
#>  1 2010 Q1 x      1.04  
#>  2 2010 Q2 x     -0.450 
#>  3 2010 Q3 x     -0.709 
#>  4 2010 Q4 x      0.0304
#>  5 2011 Q1 x     -0.450 
#>  6 2011 Q2 x      0.671 
#>  7 2011 Q3 x      1.77  
#>  8 2011 Q4 x      0.635 
#>  9 2012 Q1 x      0.368 
#> 10 2012 Q2 x      1.38  
#> # ℹ 20 more rows

# create a tsibble with multiple variables for key
tsibble(
  mth = rep(yearmonth("2010 Jan") + 0:8, each = 3),
  xyz = rep(c("x", "y", "z"), each = 9),
  abc = rep(letters[1:3], times = 9),
  value = rnorm(27),
  key = c(xyz, abc)
)
#> Using `mth` as index variable.
#> # A tsibble: 27 x 4 [1M]
#> # Key:       xyz, abc [9]
#>         mth xyz   abc    value
#>       <mth> <chr> <chr>  <dbl>
#>  1 2010 Jan x     a     -1.24 
#>  2 2010 Feb x     a     -1.23 
#>  3 2010 Mar x     a      0.115
#>  4 2010 Jan x     b     -1.06 
#>  5 2010 Feb x     b      0.229
#>  6 2010 Mar x     b      1.50 
#>  7 2010 Jan x     c     -1.04 
#>  8 2010 Feb x     c      0.622
#>  9 2010 Mar x     c     -0.574
#> 10 2010 Apr y     a     -1.17 
#> # ℹ 17 more rows

# create a tsibble containing "key" and "index" as column names
tsibble(!!!list(
  index = rep(yearquarter("2010 Q1") + 0:9, 3),
  key = rep(c("x", "y", "z"), each = 10),
  value = rnorm(30)),
  key = key, index = index
)
#> # A tsibble: 30 x 3 [1Q]
#> # Key:       key [3]
#>      index key    value
#>      <qtr> <chr>  <dbl>
#>  1 2010 Q1 x     -0.481
#>  2 2010 Q2 x      0.897
#>  3 2010 Q3 x     -0.519
#>  4 2010 Q4 x     -0.903
#>  5 2011 Q1 x      1.06 
#>  6 2011 Q2 x      1.60 
#>  7 2011 Q3 x      0.960
#>  8 2011 Q4 x     -0.142
#>  9 2012 Q1 x     -0.985
#> 10 2012 Q2 x      0.287
#> # ℹ 20 more rows