roll_max: Roll Max
In MazamaRollUtils: Efficient Rolling Functions

Description Usage Arguments Details Value Examples

Apply a moving-window maximum function to a numeric vector.

roll_max(
  x,
  width = 1L,
  by = 1L,
  align = c("center", "left", "right"),
  na.rm = FALSE
)

`x`	Numeric vector.
`width`	Integer width of the rolling window.
`by`	Integer shift to use when sliding the window to the next location
`align`	Character position of the return value within the window. One of: `"left" \| "center" \| "right"`.
`na.rm`	Logical specifying whether `NA` values should be removed before the calculations within each window.

For every index in the incoming vector x, a value is returned that is the maximum of all values in x that fall within a window of width width.

The align parameter determines the alignment of the return value within the window. Thus:

align = -1 [*------] will cause the returned vector to have width-1 NA values at the right end.
align = 0 [---*---] will cause the returned vector to have width/2 NA values at either end.
align = 1 [------*] will cause the returned vector to have width-1 NA values at the left end.

For large vectors, theby parameter can be used to force the window to jump ahead by indices for the next calculation. Indices that are skipped over will be assigned NA values so that the return vector still has the same length as the incoming vector. This can dramatically speed up calculations for high resolution time series data.

Numeric vector of the same length as x.

library(MazamaRollUtils)

# Example air quality time series
t <- example_pm25$datetime
x <- example_pm25$pm25

plot(t, x, pch = 16, cex = 0.5)
lines(t, roll_max(x, width = 12), col = 'red')
lines(t, roll_min(x, width = 12), col = 'deepskyblue')
title("12-hr Rolling Max and Min")

plot(t, x, pch = 16, cex = 0.5)
points(t, roll_max(x, width = 12, na.rm = TRUE),
       pch = 16, col = 'red')
points(t, roll_max(x, width = 12, na.rm = FALSE),
       pch = 16, col = adjustcolor('black', 0.4))
legend("topright", pch = c(1, 16),
       col = c("red", adjustcolor("black", 0.4)),
       legend = c("na.rm = TRUE", "na.rm = FALSE"))
title("12-hr Rolling max with/out na.rm")