get_extrema: Get idxs and values of extreme points in discrete sequence of...

In manuelbickel/textility: Utility functions for text mining

Get idxs and values of extreme points in discrete sequence of numbers

Description

The function uses a sliding window of size 3 to identify extreme points via zoo::rollapply . It is designed for finding extreme points in smoothing functions, e.g., loess. In this kind of sequences it may be assumed that in most cases two consectutive entries do not have the same value. In the other rare cases a portion of -1e-12 of the difference between two points is substracted from the first point, so that for longer sequences of same values always the second one will be marked as extreme point.

Usage

get_extrema(x, format_output = c("boolean", "idxs_values"))

Arguments

x	A numeric vector to be analyzed for extreme points.
format_output	May be set to "boolean" or "idxs_values". "boolean" returns boolean vectors with TRUE for local maxima and minima positions in x. "idxs_values" returns the number, indices and asociated values of maxima and minima.

Value

A list storing the boolean positions of extrema or the number, indices and asociated values of maxima and minima. List style was currently chosen to allow direct use in data.table, e.g. DT[, c("minima", "maxima"):= get_extrema(column, "boolean")]. If ouptut is required as data.table simply do as.data.table(get_extrema(...)).

Examples

get_extrema(c(0,1,0,2,0,3), "boolean")
# $minima_boolean
# [1] FALSE FALSE  TRUE FALSE  TRUE FALSE
# $maxima_boolean
# [1] FALSE  TRUE FALSE  TRUE FALSE FALSE

get_extrema(c(0,1,0,2,0,3), "idxs_values")
# $minima_n
# [1] 2
# $minima_idxs
# $minima_idxs[[1]]
# [1] 3 5
# $minima_values
# $minima_values[[1]]
# [1] 0 0
# $maxima_n
# [1] 2
# $maxima_idxs
# $maxima_idxs[[1]]
# [1] 2 4
# $maxima_values
#' # $maxima_values[[1]]
#' # [1] 1 2
#output as data.table
as.data.table(get_extrema(c(0,1,1,1,0), "idxs_values")) #<- second "1" is marked as extreme point
  minima_n minima_idxs minima_values maxima_n maxima_idxs maxima_values
1:        0          NA            NA        1           3             1

manuelbickel/textility documentation built on Nov. 25, 2022, 9:07 p.m.