R Animation Tip: Creating Pauses

Improve your R animations by implementing pause frames for emphasis

Mastering Animation in R

Over the last couple years Iā€™ve developed a multitude of animations using R. During this process Iā€™ve learned quite a bit about R graphics, gpplot2, and useful techniques in animation. In fact I presented on methods for animation in R at satRdays DC - slides available here

One simple technique to improving animations is the addition of pauses. Pauses are an effective method of capturing the viewerā€™s attention and driving home the main message of an animation. Pausing at the end of an animation (before it loops) offers the viewer the full scope of the visualization, and pauses during the animation can be used to emphasize key data points.

Letā€™s walk through creating a pause in R.

Creating Pauses in R - Libraries and Data Reshaping

Weā€™ll use the txhousing data set in the ggplot2 package to demonstrate - this data set contains information regarding the housing market in Texas provided by the TAMU real estate center. The animation will plot the median sale price of two cities - Abilene and Amarillo - from 2000 to 2015.

In my satuRdays DC presentation I covered the steps taken to develop an R animation:

  1. Interpolate your data

  2. Structure your data to create frames that move across the dimension of interest

  3. Determine plot aspects that require consistency across the animation (annotations, scales, legends, etc)

  4. Append and export the frames

The variable year contains the unique data values across our animation

  • split will generate a list of data frames we can apply interpolations to using the tweenr package.
R Libraries and Data Reshaping 
    library(ggplot2)
    library(scales)
    library(extrafont)
    library(dplyr)
    library(tweenr)
    library(lubridate)
    library(animation)
    library(RColorBrewer)
    library(grid)
    loadfonts()


    # create data frame from txhousing data included in ggplot2 package
    txHousingData <- txhousing %>% filter(city %in% unique(txhousing$city)[1:2] & month==1)
    txHousingData <- txHousingData[,c(1,2,6)]
    txHousingData$city <- factor(txHousingData$city, levels = c("Abilene","Amarillo"), labels = c("Abilene","Amarillo"))

    # determine the unique data values that tweenr will iterate over (in this case year)
    txList <- split(txHousingData,txHousingData$year)

    # Apply tweenr to interpolate frames between data points
    txTweenedData <- tween_states(txList, tweenlength= 1, statelength=0, ease='linear',nframes=200)

Since our data is arranged by year by default, itā€™s already structured in a fashion that moves across our dimension of interest (change over time) - so weā€™ve already completed the first two animation steps. Now that weā€™ve got our interpolated data frame txTweenedData we can focus on the plot aesthetics.

Plot Aesthetics

ggplot2 Theme and Color Palette 
    # plot aesthetics
    theme_white <- theme(text = element_text(family="Open Sans"),
                         panel.grid.major.y=element_blank(),
                         panel.grid.major.x=element_blank(),
                         panel.grid.minor.x=element_blank(),
                         panel.grid.minor.y=element_blank(),
                         axis.title.x=element_text(size=20, margin = margin(t=10)),
                         axis.title.y=element_text(size=20, margin = margin(t=10)),
                         axis.text.x=element_text(size=16),
                         axis.text.y=element_text(size=16),
                         axis.ticks = element_blank(),
                         plot.title=element_text(size=26,family = "Open Sans",lineheight=1.15),
                         plot.subtitle=element_text(size=20, margin = margin(t=20, b = -5),hjust = -0.03, family = "Open Sans"),
                         plot.caption=element_text(size=14, margin=margin(t=15,r=-15),hjust = -.03,lineheight=1.15, family = "Open Sans", face  = "italic"),
                         legend.position="none"
    )

    # color palette
    my_palette = c("#3EC7F4", "#3FA66C")

Itā€™s critical to determine plot aspects that require consistency across the animation. I like to assign this information as variable objects so that it can easily update across different frames contained in the plotting code. If these arenā€™t explicitly noted, ggplot2 will render the defaults in their place.

Plot Axes, Labels, and Titles 
    # y axis breaks and labels
    yAxisBreaks <- seq(0, 140000, by = 20000)
    yAxisLabels <- paste0(format(yAxisBreaks))
    yAxisLimits <- c(0,max(yAxisBreaks)* 1.03)
    yAxisLabels <- c(yAxisLabels[1:length(yAxisLabels)-1], paste0("$",yAxisLabels[length(yAxisLabels)]))

    # x axis breaks and labels
    xAxis <- seq(2000, 2015, by = 2)
    xAxisBreaks <- xAxis
    xAxisLimits <- c(1999.5, 2019)

    # plot text
    title <- "Median sale price of homes in Abilene and Amarillo, 2000 through 2015"
    subtitle <- ""
    caption <- "Information about the housing market in Texas provided by the TAMU real estate center, http://recenter.tamu.edu/."
    xLab <- "Year"
    yLab <- "Median sale price"

    midPoint <- round(max(txTweenedData$.frame) / 2)

    # add adjustments for line labels
    txTweenedData$LevelLabel <- as.character(txTweenedData$city)
    txTweenedData$nudge_x <- ifelse(txTweenedData$LevelLabel=="Abilene", 1.096,ifelse(txTweenedData$LevelLabel=="Amarillo",1.233,0))
    txTweenedData$nudge_y <- 0

Creating Pauses

Finally weā€™ve reached our R animation tip - and thankfully itā€™s pretty trivial! To generate pauses within an animation simply determine where the pause exists, subset your data to include that frame, and use replicate and grid.draw to repeat that frame n-times. For instance, say I wanted to pause at the midpoint of the animation to emphasize a point. Iā€™d first calculate the midpoint, then ensure that my data includes all frames until that point: subset(txTweenedData, .frame <= midPoint).

Animation Code 
    #calculate midpoint of the plot
    midPoint <- round(max(txTweenedData$.frame) / 2)

    g2 <- ggplot(data = subset(txTweenedData, .frame <= midPoint), aes(x = year, y = median, .frame = midPoint)) +
        geom_point(data = subset(txTweenedData, .frame == min(.frame)),aes(group=city, color=city), size=5) +
        geom_point(data = subset(txTweenedData, .frame == midPoint),aes(group=city, color=city), size=5) +
        geom_line(aes(group=city, color=city, cumulative = TRUE, label=LevelLabel), size=2.5) +
        scale_x_continuous(labels=xAxisBreaks, expand = c(0, 0), breaks=xAxisBreaks, limits =xAxisLimits) +
        scale_y_continuous(labels=yAxisLabels, expand = c(0, 0), breaks=yAxisBreaks,limits = yAxisLimits)
    g2

Creating Pauses in R

Once weā€™ve created this frame, replicate and grid.draw repeat that frame n-times to create a pause.

    replicate(75,grid.draw(g2))

Simple as that!

Full Animation Code within saveGIF

(NOTE: click on the gray bars to toggle collapsing the code!)

Animation Code 
    saveGIF({

      # print from tue first frame to the midpoint of the figure
      for(i in 1:midPoint) {
        g1 <-  ggplot(data = subset(txTweenedData, .frame <= i), aes(x = year, y = median, .frame = i)) +
          geom_point(data = subset(txTweenedData, .frame == min(.frame)),aes(group=city, color=city), size=5) +
          geom_line(aes(group=city, color=city, cumulative = TRUE, label=LevelLabel), size=2.5) +
          scale_x_continuous(labels=xAxisBreaks, expand = c(0, 0), breaks=xAxisBreaks, limits =xAxisLimits) +
          scale_y_continuous(labels=yAxisLabels, expand = c(0, 0), breaks=yAxisBreaks,limits = yAxisLimits) +
          theme_minimal() + theme_white + scale_color_manual(values=my_palette) +
          geom_text(data = subset(txTweenedData, .frame == i),aes(label =LevelLabel), size = 9, nudge_y = subset(txTweenedData, .frame == i)$nudge_y, nudge_x = subset(txTweenedData, .frame == i)$nudge_x, family = "Open Sans", lineheight = 0.75) +
          labs(x=xLab, y=yLab, title = title, subtitle = subtitle,
                     caption = caption)
          print(g1);
        }

      # print the midpoint 75 times to create a pause
      g2 <- ggplot(data = subset(txTweenedData, .frame <= midPoint), aes(x = year, y = median, .frame = midPoint)) +
          geom_point(data = subset(txTweenedData, .frame == min(.frame)),aes(group=city, color=city), size=5) +
          geom_point(data = subset(txTweenedData, .frame == midPoint),aes(group=city, color=city), size=5) +
          geom_line(aes(group=city, color=city, cumulative = TRUE, label=LevelLabel), size=2.5) +
          scale_x_continuous(labels=xAxisBreaks, expand = c(0, 0), breaks=xAxisBreaks, limits =xAxisLimits) +
          scale_y_continuous(labels=yAxisLabels, expand = c(0, 0), breaks=yAxisBreaks,limits = yAxisLimits) +
          theme_minimal() + theme_white + scale_color_manual(values=my_palette) +
          geom_text(data = subset(txTweenedData, .frame == midPoint),aes(label =LevelLabel), size = 9, nudge_y = subset(txTweenedData, .frame == midPoint)$nudge_y, nudge_x = subset(txTweenedData, .frame == midPoint)$nudge_x, family = "Open Sans", lineheight = 0.75) +
          labs(x=xLab, y=yLab, title = title, subtitle = subtitle,
                     caption = caption)

      replicate(75,grid.draw(g2))

      # print from tue midpoint of the figure until the last frame
      for(i in midPoint:max(txTweenedData$.frame)) {
        g3 <- ggplot(data = subset(txTweenedData, .frame <= i), aes(x = year, y = median, .frame = i)) +
          geom_point(data = subset(txTweenedData, .frame == min(.frame)),aes(group=city, color=city), size=5) +
          geom_line(aes(group=city, color=city, cumulative = TRUE, label=LevelLabel), size=2.5) +
          scale_x_continuous(labels=xAxisBreaks, expand = c(0, 0), breaks=xAxisBreaks, limits =xAxisLimits) +
          scale_y_continuous(labels=yAxisLabels, expand = c(0, 0), breaks=yAxisBreaks,limits = yAxisLimits) +
          theme_minimal() + theme_white + scale_color_manual(values=my_palette) +
          geom_text(data = subset(txTweenedData, .frame == i),aes(label =LevelLabel), size = 9, nudge_y = subset(txTweenedData, .frame == i)$nudge_y, nudge_x = subset(txTweenedData, .frame == i)$nudge_x, family = "Open Sans", lineheight = 0.75) +
          labs(x=xLab, y=yLab, title = title, subtitle = subtitle,
                     caption = caption)
        print(g3);  }

      # print the final frame of the figure 110 times to create an ending pause
      wholeFig <- ggplot(data = subset(txTweenedData, .frame <= i), aes(x = year, y = median, .frame = i)) +
          geom_point(data = subset(txTweenedData, .frame == min(.frame)),aes(group=city, color=city), size=5) +
          geom_point(data = subset(txTweenedData, .frame == i),aes(group=city, color=city), size=5) +
          geom_line(aes(group=city, color=city, cumulative = TRUE, label=LevelLabel), size=2.5) +
          scale_x_continuous(labels=xAxisBreaks, expand = c(0, 0), breaks=xAxisBreaks, limits =xAxisLimits) +
          scale_y_continuous(labels=yAxisLabels, expand = c(0, 0), breaks=yAxisBreaks,limits = yAxisLimits) +
          theme_minimal() + theme_white + scale_color_manual(values=my_palette) +
          geom_text(data = subset(txTweenedData, .frame == i),aes(label =LevelLabel), size = 9, nudge_y = subset(txTweenedData, .frame == i)$nudge_y, nudge_x = subset(txTweenedData, .frame == i)$nudge_x, family = "Open Sans", lineheight = 0.75) +
          labs(x=xLab, y=yLab, title = title, subtitle = subtitle,
                     caption = caption)

      replicate(110,grid.draw(wholeFig))
    },movie.name="/home/michael/Documents/animation_samples/txHousing/txHousing.gif",interval = .02, ani.width = 1024, ani.height = 612)

Median sale price of homes in Abilene and Amarillo, 2000 through 2015

Finally itā€™s smart to compress the final animation, since gifs can be unwieldy.

GIF Compression 
    # compress gif
    gif_compress <- function(ingif, outgif, show=TRUE, extra.opts=""){
      command <-  sprintf("gifsicle -O3 %s < %s > %s", extra.opts, ingif, outgif)
      system.fun <- if (.Platform$OS.type == "windows") shell else system
      if(show) message("Executing: ", strwrap(command, exdent = 2, prefix = "\n"))
      system.fun(ifelse(.Platform$OS.type == "windows", sprintf(""%s"", shQuote(command)), command))
    }

    gif_compress("/home/michael/Documents/animation_samples/txHousing/txHousing.gif","/home/michael/Documents/animation_samples/txHousing/tx_Housing.gif",extra.opts="--colors 256")

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