Converting lines in an svg image to csv

August 15, 2019
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During a search for data on programming language usage I discovered Stack Overflow Trends, showing an interesting plot of language tags appearing on Stack Overflow questions (see below). Where was the csv file for these numbers? Somebody had asked this question last year, but there were no answers.

Stack Overflow language tag trends over time.

The graphic is in svg format; has anybody written an svg to csv conversion tool? I could only find conversion tools for specialist uses, e.g., geographical data processing. The svg file format is all xml, and using a text editor I could see the numbers I was after. How hard could it be (it had to be easier than a png heatmap)?

Extracting the x/y coordinates of the line segments for each language turned out to be straight forward (after some trial and error). The svg generation process made matching language to line trivial; the language name was included as an xml attribute.

Programmatically extracting the x/y axis information exhausted my patience, and I hard coded the numbers (code+data). The process involves walking an xml structure and R’s list processing, two pet hates of mine (the data is for a book that uses R, so I try to do everything data related in R).

I used R’s xml2 package to read the svg files. Perhaps if my mind had a better fit to xml and R lists, I would have been able to do everything using just the functions in this package. My aim was always to get far enough down to convert the subtree to a data frame.

Extracting data from graphs represented in svg files is so easy (says he). Where is the wonderful conversion tool that my search failed to locate? Pointers welcome.

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