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Demo of Perspective, using US COVID data from https://covidtracking.com.

The Group By column is a good example of using Perspective's ExprTK column language to clean/reformat a column. The raw "date" column, as imported from https://covidtracking.com, use the date format YYYYMMDD. Using this expression, we can parse this format into a well-typed date() column, then bucket this by week to get a sensible graph:

// Parsed \"date\" bucket by week
var year := integer(floor(\"date\" / 10000));
var month := integer(floor(\"date\" / 100)) - year * 100;
var day := integer(\"date\" % 100);
bucket(date(year, month, day), 'W')