Monday, March 18, 2013

R: Reproducible Research - Watermarks in Plots

Research is an iterative process: data is constantly being acquired, cleaned, and finalized while the analysis is being conducted. Since we work in a constantly evolving data and program landscape, version control is extremely important when programming, making research decisions, drafting reports, and writing manuscripts. Thankfully, reproducible research techniques are making this easier, which can mean less version control headaches, and more productivity.  Watermarks are a quick way to improve version control and better communicate the scope of results.

The problem: Images can be abstracted and embedded, obscuring their context or data provenance. This can lead to preliminary, dummy, or simulation results being confused for a final result or privileged/confidential results being accidentally disseminated.

The solution: Image watermarks can’t be easily removed by cropping and embedding by the lay user, don’t obscure results, and provide information about data provenance and information sensitivity. These can be added in your software package of choice, so that no post-processing of images is necessary, and can be easily suppressed in final results by flag variables.

The tools:
  • mtext, text: add text to margins (mtext) or within the plot (text)
  • grconvertX, grconvertY: find coordinates in a device, independent of axes
  • rgb: create translucent text from RGB values
 Let's save our results in a date stamped.png format: first we open a new device, use the generic R plot function, and use text and mtext to add watermarks in the image.

run.date <- format(Sys.Date(), "%m-%d-%Y")
    png(paste0("Watermark 1 - ", run.date, ".png"))
    plot(rnorm(100))
    text(x = grconvertX(0.5, from = "npc"),  # align to center of plot X axis
       y = grconvertY(0.5, from = "npc"), # align to center of plot Y axis
        labels = "CONFIDENTIAL", # our watermark
        cex = 3, font = 2, # large, bold font - hard to miss
        col = rgb(1, 0, 0, .2), # translucent (0.2 = 20%) red color
        srt = 45) # srt = angle of text: 45 degree angle to X axis
    # Add another watermark in lower (side = 1) right (adj = 1) corner
    watermark <- paste("Data embargo until", run.date)
    mtext(watermark, side = 1, line = -1, adj = 1, col = rgb(1, 0, 0, .2), cex = 1.2)
dev.off() # close device, create image


The result:
 

Watermarks in ggplot2 and lattice:

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