```
#' Create a traceplot for a single desired node
#'
#' @param post an object of class \code{mcmc.list}
#' @param p_one a character vector of length 1.
#' Should be a node reference to a single element in the model. E.g., \code{"pi[1]"}, not \code{"pi"}.
#' @param thin_percent a numeric vector of length one and scaled between 0 and 1.
#' of samples you'd like to remove before traceplotting. If saving as a pdf,
#' these files can get very large with many samples and render slowly.
#' Samples are thinned systematically (i.e., at evenly-spaced intervals).
#'
#' @export
trace_plot = function(post, p_one, thin_percent = 0) {
# return error if p_one has length > 1
if (length(p_one) > 1) stop ("p_one must have only one element, and it must match the desired node exactly")
# lock in the search string. It must be exact for the rest of this code to work
p_one = ins_regex_lock(p_one)
# perform additional thinning if desired
post = post_thin(post, thin_percent = thin_percent)
# extract this node's samples
post_sub = post_subset(post, p_one, matrix = T, iters = T, chains = T)
# get axis limits
y_lim = range(post_sub[,3])
# set up graphics device
par(mar = c(1.5,0.5,2.5,2), tcl = -0.25,
mgp = c(1.5,0.4,0), yaxs = "r")
# create an empty plotting region
plot(1,1, axes = F, type = "n",
xlim = range(post_sub[,"ITER"]),
ylim = y_lim, xlab = "", ylab = "")
# loop through chains plotting the trace of each
sapply(unique(post_sub[,"CHAIN"]), function(c) {
chain_sub = post_sub[post_sub[,"CHAIN"] == c,]
lines(chain_sub[,3] ~ chain_sub[,"ITER"], col = c)
})
axis(side = 1); axis(side = 4)
box()
}
```

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