In Nowosad/pollen: Analysis of Aerobiological Data

knitr::opts_chunk$set(collapse = T, comment = "#>")

pollen is a set of functions for working with aerobiological data. It takes care of some of the most widely use aerobiological calculations, such as determination of pollen season limits or replacement of outliers in a pollen count data.

library(pollen)

Examples

In the examples below, we will use the pollen_count dataset available in the pollen package. It has five variables:

site - a name of the aerobiological monitoring site (one of "Atlantis", "Hundred Acre Wood", "Oz", "Shire")
date - a date of the measurement
alder - pollen concentration of alder (grains/m3)
birch - pollen concentration of birch (grains/m3)
hazel - pollen concentration of hazel (grains/m3)

data("pollen_count")
head(pollen_count)

Pollen season

The most important function in this package, pollen_season() determines pollen season limits. It can be calculated independently for each site, for example Oz:

df <- subset(pollen_count, site == "Oz")
pollen_season(value = df$birch, date = df$date, method = "95")

... and Atlantis:

df2 <- subset(pollen_count, site == "Atlantis")
pollen_season(value = df2$alder, date = df2$date, method = "95")

NA is returned for years with missing values in the data, as you can see above.

In combination with the purrr package (or the base apply() function), it is possible to calculate pollen season limits for many sites:

library(purrr)
pollen_count %>%
  split(., .$site) %>%
  map_dfr(~pollen_season(value = .$hazel, date = .$date, method = "95"), .id = "site")

Comparision of the pollen season methods

Next possibility is to compare many methods for determination of pollen season limits for one measurement site. Let's try it for Oz:

df <- subset(pollen_count, site == "Oz")

We just need to provide a vector of names with the methods and use it in the map_dfr() function:

ps_methods <- c("90", "95", "98", "Mesa", "Jager", "Lejoly")
names(ps_methods) <- ps_methods
df_seasons <- ps_methods %>%
  map_dfr(~pollen_season(method = ., value = df$birch, date = df$date), .id = "method")
head(df_seasons)

Replacement of outliers

The pollen package also implements a method for replacement of outliers (Kasprzyk and Walanus (2014) <doi:10.1007/s10453-014-9332-8>) with the outliers_replacer() function. outliers_replacer() accepts a column with concentration, a column with date, and a threshold - a number indicating how many times outlying value needs to be larger than the background to be replaced. This method can be applied on a single site:

df <- subset(pollen_count, site == "Shire")
new_df <- outliers_replacer(value = df$alder, date = df$date)
identical(df, new_df)

Or a group of sites:

library(purrr)
new_pollen_count <- pollen_count %>%
  split(., .$site) %>%
  map_dfr(~outliers_replacer(value = .$hazel, date = .$date, threshold = 4))