Author: Kevin R. Coombes

# Using Polychrome With ggplot

#### Kevin R. Coombes

In this vignette, we describe how to use `Polychrome` palettes with the package `ggplot2`. The vignette will only run code if the `ggplot2` package is available.

    evalVignette <- requireNamespace("ggplot2", quietly = TRUE)
    knitr::opts_chunk$set(eval = evalVignette)

## Getting Started

We want to build a custom palette of 40 colors for this application, with each block of four consecutive colors being distinguishable. We start by constructing a new palette in the usual way.

    library(Polychrome)
    set.seed(935234)
    P40 <- createPalette(40, c("#FF0000", "#00FF00", "#0000FF"), range = c(30, 80))
    swatch(P40)

We achieve the goal of making the blocks of four colors being distinguishable by first sorting by hue, and then rearranging them into four-blocks.

    P40 <- sortByHue(P40)
    P40 <- as.vector(t(matrix(P40, ncol=4)))
    swatch(P40)

Here is the key point of this entire vignette: By default, `Polychrome` gives names to each of the colors in a palette. But, in `ggplot`, named colors will only be applied if they match the levels of an appropriate factor in the data. The simplest solution is to remove the names:

    names(P40) <- NULL

## Simulating Complex Data

For illustration purposes, we simulate a data set with a moderately complex structure. Specifically, we assume that we have

- Nine groups of samples,
- Four samples in each group,
- Three replicate experiments for each sample, and
- Measurements repeated over four days.

Here is the simulated design of the data set.

    ## Nine groups
    NG <- 9
    gp <- paste("G", 1:NG, sep = "")
    length(gp)

    ## [1] 9

    ## Four Subjects per group
    ## 36 Subjects = 9 groups * 4 subjects/group
    sid <- paste(rep(LETTERS[1:2], each=26), c(LETTERS, LETTERS), sep="")[1:(4*NG)]
    length(sid)

    ## [1] 36

    ## Three Reps per subject
    ## 108 Experiments
    reps = factor(rep(c("R1", "R2", "R3"), times = length(sid)))
    length(reps)

    ## [1] 108

    ## Each experiment with measurements on four Days, so 432 data rows
    daft <- data.frame(Day = rep(1:4, each=length(reps)),
                       Group = factor(rep(rep(gp, each=12), times = 4)),
                       Subject = factor(rep(rep(sid, each = 3), times=4)),
                       Rep = factor(rep(reps, times = 4)))
    dim(daft)

    ## [1] 432   4

    summary(daft)

    ##       Day           Group        Subject    Rep
    ##  Min.   :1.00   G1     : 48   AA     : 12   R1:144
    ##  1st Qu.:1.75   G2     : 48   AB     : 12   R2:144
    ##  Median :2.50   G3     : 48   AC     : 12   R3:144
    ##  Mean   :2.50   G4     : 48   AD     : 12
    ##  3rd Qu.:3.25   G5     : 48   AE     : 12
    ##  Max.   :4.00   G6     : 48   AF     : 12
    ##                 (Other):144   (Other):360

Now we add simulated “measurements” taken on each replicate of each subject on each of four days.

    ## Linear model with noise, ignoring group
    beta <- runif(length(sid), 0.5, 2)
    ## "Measured" variable
    attach(daft)
    daft$variable <- rnorm(nrow(daft), 0, 0.2) + 1  + beta[as.numeric(Subject)]*Day
    detach()

### Plotting the results.

    library(ggplot2)
    ggplot(daft, aes(x = Day, y = variable, colour = as.factor(Subject))) +
      geom_point(aes(shape = as.factor(Rep)), size = 3) +
      geom_line(aes(linetype = as.factor(Rep)), size = 0.8) +
      facet_wrap(. ~ Group, ncol = 3)+
      theme_bw() + theme(legend.position="none")+
      scale_color_manual(values = P40)

    ## Warning: Using `size` aesthetic for lines was deprecated in ggplot2 3.4.0.
    ## ℹ Please use `linewidth` instead.
    ## This warning is displayed once per session.
    ## Call `lifecycle::last_lifecycle_warnings()` to see where this warning was
    ## generated.

A faceted plot, colored by subject.