day_night_flag: Day/night flag

In dataprep: Fast, Efficient, and Versatile Data Preprocessing and Reshaping with 'C++', 'OpenMP' & 'SIMD'

Day/night flag

Description

Creates a day/night indicator for each time point. If latitude and longitude are not provided, local time is used (daylight defined by an hour threshold). Otherwise, an approximate solar zenith angle is computed to determine whether the sun is above the horizon.

Usage

day_night_flag(data, date_col = NULL, lat = NULL, lon = NULL,
               threshold = 6, type = c("binary", "sun", "shade"),
               local_tz = "UTC", verbose = FALSE)

Arguments

data	A data frame with a time column.
date_col	Time column index or name. If NULL, the first column matching date is used.
lat	Latitude of the location(s). Can be a scalar or a vector of length equal to the number of rows.
lon	Longitude of the location(s). Same behavior as lat.
threshold	Hour threshold used for local-time based classification (default 6). Only used if latitude/longitude are missing.
type	Output type: "binary" returns 1/0, "sun" returns "day"/"night", "shade" returns "day"/"shade".
local_tz	Time zone for local time calculation (default UTC).
verbose	Logical; if TRUE, prints progress message.

Details

When latitude/longitude are supplied, the function computes the solar zenith angle using a simplified astronomical formula. Values with a solar zenith angle below 90 degrees are considered day.

Value

A vector of day/night flags.

Author(s)

Chun-Sheng Liang <[e-mail]>

References

1. Example data is from https://smear.avaa.csc.fi/download. It includes particle number concentrations in SMEAR I Varrio forest.

Examples

day_night_flag(data[1:100, c(1, 4, 17:19)], date_col = 1, lat = 40, lon = -105)

dataprep documentation built on Oct. 1, 2026, 5:07 p.m.