hist2d: 2-Dimensional Histogram
In artidata/artidata.viz: Artidata's Personal Data Visualization Package

2D Histogram is an alternative to traditional scatter plot. Similar with histogram, it constructs bins of regular size, and count the number of observations found in each bin. However, 2 dimensions are involved in the binning. It also use colour gradient instead of bar height to represent the count number. This plotting technique will be more useful when many of the points are overlapped, or even stacked in the scatter plot (overplotting).

hist2d(
  dt,
  x,
  y,
  title,
  labX,
  labY,
  limX,
  limY,
  facet = 0,
  z = NULL,
  widthBin,
  nBin,
  hasLine = F,
  statsLine = c("count", "rsquare", "signif"),
  palette = "Reds",
  theme = "minimal",
  hasGrid = F,
  trans = "identity"
)

`dt`	Data in the class of `data.table`. Currently, has name `.x` or `.y`
`x, y`	The name of the columns in the `dt` that will be used as coordinates of the 2D histogram. The columns selected must be of numeric vectors. These are `(x,y)` coordinates when constructing a scatter plot. If `x` and/or `y` is not supplied, the first and/or second column of `dt` will be used.
`labX, labY`	Axis label(s) for the plot output. If not supplied, the value(s) of `x` or `y` will be used.
`limX, limY`	The limits of coordinates of x or y axis that will be shown in the plot. It does not change the regression line if `hasLine` is `TRUE`. If not supplied, The values will be the minimum and the maximum value of corresponding dimension.
`facet`	Any of `{0,1,2}`. It refers to the ggplot2's faceting technique. Multiple 2D histograms will be displayed as a sequence of panels which enables grouping comparison. The value represents the number of additional categorical variable(s).
`z`	A vector of column name(s) of `dt` that will be used for faceting. The length of the vector must match the number in `facet`. Please, set it to `NULL` when `facet==0`.
`widthBin`	If not supplied, Freedman and Diaconis’s rule is applied to each dimension.
`nBin`	The number of bins to span the length from minimum to maximum point of each coordinate. If it is a single integer `n`, both x and y will be spanned by `n` bins each. If it is an integer vector of length 2 (i.e. `c(m,n)`), `m` bins will spanned the x coordineates, vice versa.
`hasLine`	logical with `FALSE` as the default. If `TRUE`, draw and annotate a simple linear regression line of `y` against `x`
`palette`	Color scheme choices as specified in http://colorbrewer2.org

library(data.table)
library(ggplot2)
library(scales)

set.seed(240193)

N=10000

dtA=data.table(x=runif(N,-3,3),y=runif(N,-3,3),z="A")

dtB=data.table(x=rnorm(N),y=rnorm(N),z="B")

dtC=data.table(x=seq(-3,3,length.out = N))
dtC[,":="(y=0.5*x+rnorm(N,sd=0.5),z="C"),]

dtD=data.table(x=c(rnorm(N/2,-1,.75),rnorm(N/2,1,.75)),
               y=c(rnorm(N/2,1,.75),rnorm(N/2,-1,.75)),
               z="D")

dt1=rbindlist(list(dtA,dtB,dtC,dtD))

hist2d(dt1,facet=1)

dt2=data.table(height=c(1.47,1.50,1.52,1.55,1.57,
                        1.60,1.63,1.65,1.68,1.70,
                        1.73,1.75,1.78,1.80,1.83),
               mass=c(52.21,53.12,54.48,55.84,57.20,
                      58.57,59.93,61.29,63.11,64.47,
                      66.28,68.10,69.92,72.19,74.46))
slr(dt2,"x","y","z")