The digitize Package: Extracting Numerical Data from Scatterplots
Timothée Poisot · The R Journal · 2011
Abstract I present the small R package digitize, designed to extract data from scatterplots with a simple method and suited to small datasets. I present an application of this method to the ex-traction of data from a graph whose source is not available. The package digitize, that I present here, allows a user to load a graphical file of a scatterplot (with the help of the read.jpeg function of the ReadImages package) in the graphical window of R, and to use the locator function to calibrate and extract the data. Calibration is done by setting four reference points on the original graph axis, two for the x values and two for the y values. The use of four points for cal-ibration is justified by the fact that it makes calibra-tions on the axis possible, as y data are not taken into account for calibration of the x axis, and vice versa. This is useful when working on data that are not available in digital form, e.g. when integrating old papers in meta-analyses. Several commercial or free software packages allow a user to extract data from a plot in image format, among which we can cite