SO questions I often come back to:
https://stackoverflow.com/questions/8508482/what-does-sd-stand-for-in-data-table-in-r/47406952#47406952
https://stackoverflow.com/questions/22408306/using-i-to-return-row-numbers-with-data-table-package
https://stackoverflow.com/questions/3505701/grouping-functions-tapply-by-aggregate-and-the-apply-family
https://stackoverflow.com/questions/22937618/reference-what-does-this-regex-mean
https://stackoverflow.com/questions/9471906/what-are-the-differences-between-community-detection-algorithms-in-igraph
https://stackoverflow.com/questions/32504313/how-to-add-horizontal-lines-showing-means-for-all-groups-in-ggplot2
https://stackoverflow.com/questions/13961913/which-layout-should-i-use-to-get-non-overlapping-edges-in-igraph