Count Consecutive Sequences of Events

Run length encoding to detect consecutive sequences of events.

rle2(x, index, l_run, value)

Source

Raphael Saldanha, https://rfsaldanha.github.io/posts/run_length_encoding.html with modifications by Adam Sparks (DPIRD).

Arguments

x

A vector of values to check for consecutive sequences of events.

index

A index of event values, e.g. a vector of date values.

l_run

A integer value indicating the length of the run for the period of interest.

value

The base value to check against, for which values greater than will be recorded as TRUE.

Value

A data.table with three columns, the ‘index’, ‘x’, the original value that was tested and ‘test’ a column of Boolean

values indicating whether the event was TRUE (greater than value) or FALSE (less than value), “test”.

Note

R already has an base::rle(), so this function is suffixed with 2 to avoid NAMESPACE clashes.

Author

Adam Sparks, adamhsparks@gmail.com

Examples

# Get rainfall data since 2017 for Northam
library(weatherOz)
library(theme.dpird)
library(scales)

wd <- get_dpird_summaries(
  station_code = "NO",
  start_date = "20170101",
  end_date = "20171231",
  api_key = Sys.getenv("DPIRD_API_KEY"),
  interval = "daily",
)

# Determine where runs of 2 or more days with rain over 0.5mm occur
rain <- rle2(
  x = wd$rainfall,
  index = wd$date,
  l_run = 2,
  value = 0.5
)

# Plot rainfall values
ggplot(data = rain, aes(x = index, y = value)) +
  geom_line(colour = dpird_cols("light blue"), alpha = 0.7) +
  geom_point(aes(color = test), alpha = 0.85) +
  scale_color_manual(values = unname(dpird_cols(c("mid blue", "dark red")))) +
  theme_dpird() +
  scale_x_date(labels = date_format("%m-%Y")) +
  xlab("Date") +
  ylab("Rainfall (mm)") +
 guides(colour = guide_legend("Two or more consecutive days of rain")) +
  theme(legend.position = "bottom", legend.direction = "horizontal")


# Determine where runs of 2 or more days avg temp above 28 C occur
tavg <- rle2(
  x = wd$air_tavg,
  index = wd$date,
  l_run = 2,
  value = 28
)

# Plot rainfall values
ggplot(data = tavg, aes(x = index, y = value)) +
  geom_line(colour = dpird_cols("light blue"), alpha = 0.7) +
  geom_point(aes(color = test), alpha = 0.85) +
  scale_color_manual(values = unname(dpird_cols(c("mid blue", "dark red")))) +
  geom_hline(yintercept = 28, colour = dpird_cols("dark red")) +
  theme_dpird() +
  scale_x_date(labels = date_format("%m-%Y")) +
  xlab("Date") +
  ylab("Temperature (˚C)") +
  guides(colour = guide_legend("Four or more consecutive days above 28˚ C")) +
  theme(legend.position = "bottom", legend.direction = "horizontal")