Add sparkline support

[bgreenwell]

Minimal example:

# Load required packages
library(dplyr)
library(ranger)
library(pdp)
library(vip)
library(sparkline)
library(DT)
library(htmlwidgets)

# Feature importance and feature effects from a random forest fit to the Boston
# housing data
set.seed(101)
fit <- ranger(cmedv ~ ., data = pdp::boston)
vi_scores <- vi(fit, method = "pdp", sort = FALSE)
pdps <- attr(vi_scores, which = "pdp")
# ylim <- range(as.numeric(sapply(pdps, FUN = function(x) range(x$yhat))))

# Prep data for sparklines
vi_scores$Effect <- NA
for (i in seq_len(nrow(vi_scores))) {
  vi_scores[["Effect"]][i] <- 
    paste(pdps[[vi_scores$Variable[i]]][["yhat"]], collapse = ",")
}
vi_scores$Importance <- round(vi_scores$Importance, digits = 3)
vi_scores <- arrange(vi_scores, desc(Importance))

columnDefs = list(list(
  targets = 3,
  render = JS("function(data, type, full){
    return '<span class=spark>' + data + '</span>'           
  }")
))

fnDrawCallback = JS("function (oSettings, json) {
  $('.spark:not(:has(canvas))').sparkline('html', {
    type: 'line',
    highlightColor: 'orange'
  });
}")

d <- datatable(vi_scores, options = list(
  columnDefs = columnDefs,
  fnDrawCallback = fnDrawCallback
))
d$dependencies <- append(d$dependencies, htmlwidgets:::getDependency('sparkline'))
d