slider: summary-index – R documentation

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summary-index

Specialized sliding functions relative to an index

Description

These functions are specialized variants of the most common ways that slide_index() is generally used. Notably, slide_index_sum() can be used for rolling sums relative to an index (like a Date column), and slide_index_mean() can be used for rolling averages.

These specialized variants are much faster and more memory efficient than using an otherwise equivalent call constructed with slide_index_dbl() or slide_index_lgl(), especially with a very wide window.

Usage

slide_index_sum(
  x,
  i,
  ...,
  before = 0L,
  after = 0L,
  complete = FALSE,
  na_rm = FALSE
)

slide_index_prod(
  x,
  i,
  ...,
  before = 0L,
  after = 0L,
  complete = FALSE,
  na_rm = FALSE
)

slide_index_mean(
  x,
  i,
  ...,
  before = 0L,
  after = 0L,
  complete = FALSE,
  na_rm = FALSE
)

slide_index_min(
  x,
  i,
  ...,
  before = 0L,
  after = 0L,
  complete = FALSE,
  na_rm = FALSE
)

slide_index_max(
  x,
  i,
  ...,
  before = 0L,
  after = 0L,
  complete = FALSE,
  na_rm = FALSE
)

slide_index_all(
  x,
  i,
  ...,
  before = 0L,
  after = 0L,
  complete = FALSE,
  na_rm = FALSE
)

slide_index_any(
  x,
  i,
  ...,
  before = 0L,
  after = 0L,
  complete = FALSE,
  na_rm = FALSE
)

Arguments

`x`	`[vector]` A vector to compute the sliding function on. For sliding sum, mean, prod, min, and max, `x` will be cast to a double vector with `vctrs::vec_cast()`. For sliding any and all, `x` will be cast to a logical vector with `vctrs::vec_cast()`.
`i`	`[vector]` The index vector that determines the window sizes. It is fairly common to supply a date vector as the index, but not required. There are 3 restrictions on the index: The size of the index must match the size of `.x`, they will not be recycled to their common size. The index must be an increasing vector, but duplicate values are allowed. The index cannot have missing values.
`...`	These dots are for future extensions and must be empty.
`before`	`[vector(1) / function / Inf]` If a vector of size 1, these represent the number of values before or after the current element of `.i` to include in the sliding window. Negative values are allowed, which allows you to "look forward" from the current element if used as the `.before` value, or "look backwards" if used as `.after`. Boundaries are computed from these elements as `.i - .before` and `.i + .after`. Any object that can be added or subtracted from `.i` with `+` and `-` can be used. For example, a lubridate period, such as `lubridate::weeks()`. If `Inf`, this selects all elements before or after the current element. If a function, or a one-sided formula which can be coerced to a function, it is applied to `.i` to compute the boundaries. Note that this function will only be applied to the unique values of `.i`, so it should not rely on the original length of `.i` in any way. This is useful for applying a complex arithmetic operation that can't be expressed with a single `-` or `+` operation. One example would be to use `lubridate::add_with_rollback()` to avoid invalid dates at the end of the month. The ranges that result from applying `.before` and `.after` have the same 3 restrictions as `.i` itself.
`after`	`[vector(1) / function / Inf]` If a vector of size 1, these represent the number of values before or after the current element of `.i` to include in the sliding window. Negative values are allowed, which allows you to "look forward" from the current element if used as the `.before` value, or "look backwards" if used as `.after`. Boundaries are computed from these elements as `.i - .before` and `.i + .after`. Any object that can be added or subtracted from `.i` with `+` and `-` can be used. For example, a lubridate period, such as `lubridate::weeks()`. If `Inf`, this selects all elements before or after the current element. If a function, or a one-sided formula which can be coerced to a function, it is applied to `.i` to compute the boundaries. Note that this function will only be applied to the unique values of `.i`, so it should not rely on the original length of `.i` in any way. This is useful for applying a complex arithmetic operation that can't be expressed with a single `-` or `+` operation. One example would be to use `lubridate::add_with_rollback()` to avoid invalid dates at the end of the month. The ranges that result from applying `.before` and `.after` have the same 3 restrictions as `.i` itself.
`complete`	`[logical(1)]` Should the function be evaluated on complete windows only? If `FALSE`, the default, then partial computations will be allowed.
`na_rm`	`[logical(1)]` Should missing values be removed from the computation?

Details

For more details about the implementation, see the help page of slide_sum().

Value

A vector the same size as x containing the result of applying the summary function over the sliding windows.

For sliding sum, mean, prod, min, and max, a double vector will be returned.
For sliding any and all, a logical vector will be returned.

Examples

x <- c(1, 5, 3, 2, 6, 10)
i <- as.Date("2019-01-01") + c(0, 1, 3, 4, 6, 8)

# `slide_index_sum()` can be used for rolling sums relative to an index,
# allowing you to "respect gaps" in your series. Notice that the rolling
# sum in row 3 is only computed from `2019-01-04` and `2019-01-02` since
# `2019-01-01` is more than two days before the current date.
data.frame(
  i = i,
  x = x,
  roll = slide_index_sum(x, i, before = 2)
)

# `slide_index_mean()` can be used for rolling averages
slide_index_mean(x, i, before = 2)

# Only evaluate the sum on windows that have the potential to be complete
slide_index_sum(x, i, before = 2, after = 1, complete = TRUE)

slider

Sliding Window Functions

v0.2.1

MIT + file LICENSE

Authors

Davis Vaughan [aut, cre], RStudio [cph]

Initial release