Frequently Asked Questions
How do I fit a custom distribution?
The user can also specify a custom distribution (called say
dist) provided the following functions are defined:
- probability density (
ddist(x, par1, par2, log = FALSE))
- cumulative distribution (
pdist(q, par1, par2, lower.tail = TRUE, log.p = FALSE))
- inverse cumulative distribution (
qdist(p, par1, par2, lower.tail = TRUE, log.p = FALSE))
- random samples (
rdist(n, par1, par2))
- starting values (
How do I fit distributions to multiple groups such taxa and/or chemicals?
An elegant approach using some tidyverse packages is demonstrated below.
boron_preds <- nest(ssdtools::boron_data, data = c(Chemical, Species, Conc, Units)) %>%
Fit = map(data, ssd_fit_dists, dists = "lnorm"),
Prediction = map(Fit, predict)
The resultant data and predictions can then be plotted as follows.
ssd_plot(boron_data, boron_preds, xlab = "Concentration (mg/L)", ci = FALSE) +
How do I plot a Cullen Frey plot?
The data can be visualized using a Cullen Frey plot of the skewness and kurtosis.
How do I plot model diagnostics?
fitdists object can be plotted to display model diagnostics plots for each fit.