Sample draws from a tidy-format data frame of draws
Given a tidy-format data frame of draws with a column indexing each draw, subsample the data frame to a given size based on a column indexing draws, ensuring that rows in sub-groups of a grouped data frame are sampled from the same draws.
sample_draws(data, n, draw = ".draw")
data |
Data frame to sample from |
n |
The number of draws to select |
draw |
The name of the column indexing the draws |
sample_draws() makes it easier to sub-sample a grouped, tidy-format data frame of draws. On a grouped data frame,
the naive approach of using filter with the .draw column will give incorrect results as it will
select a different sample within each group. sample_draws() ensures the same sample is selected within
each group.
Matthew Kay
library(ggplot2)
library(dplyr)
if (
require("brms", quietly = TRUE) &&
require("modelr", quietly = TRUE)
) {
theme_set(theme_light())
m_mpg = brm(mpg ~ hp * cyl, data = mtcars,
# 1 chain / few iterations just so example runs quickly
# do not use in practice
chains = 1, iter = 500)
# draw 100 fit lines from the posterior and overplot them
mtcars %>%
group_by(cyl) %>%
data_grid(hp = seq_range(hp, n = 101)) %>%
add_fitted_draws(m_mpg) %>%
sample_draws(100) %>%
ggplot(aes(x = hp, y = mpg, color = ordered(cyl))) +
geom_line(aes(y = .value, group = paste(cyl, .draw)), alpha = 0.25) +
geom_point(data = mtcars)
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