Objective: Use tidyr to organize a collection of references by key topics

The idea is to choose characteristics used to compare and categorize a set of peer-reviewed papers. The papers are identified by doi and by a an ID column internal to the data set, which is entered in spreadsheet software like Excel. Entering one value per row simplifies data entry.

For each characteristic, a value is entered from one of a defined set (this can be done by either creating data validation or by accepting autocomplete for values that have already been entered. The idea is that these entries provide a defined number of values. Some data entered might be numerical.

Here this approach is demonstrated with a collection collected in late 2021 and comprised of of 27 papers on studies of moth chemical ecology using y-tube olfactometers.