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Heat maps

Explore this snippet with some demo data here.

Description

Heatmaps are a great way to visualize the relationship between two variables enumerated across all possible combinations of each variable. To create one, your data must contain

  • 2 categorical columns (e.g. not numeric columns)
  • 1 numerical column
SELECT 
   AGG_FN(<COLUMN>) as metric,
   <CAT_COLUMN1> as cat1,
   <CAT_COLUMN2> as cag2,
FROM 
   <PROJECT.SCHEMA.TABLE>
GROUP BY
   cat1, cat2

where:

  • AGG_FN is an aggregation function like SUM, AVG, COUNT, MAX, etc.
  • COLUMN is the column you want to aggregate to get your metric. Make sure this is a numeric column. Must add up to 1 for each bar.
  • CAT_COLUMN1 and CAT_COLUMN2 are the groups you want to compare. One will go on the x axis and the other on the y-axis. Make sure these are categorical or temporal columns and not numerical fields.

Usage

In this example with some Spotify data, we'll see the average daily streams across different days of the week and months of the year.

-- a
select sum(streams) daily_streams, day from spotify.spotify_daily_tracks group by day
daily_streams day
234109876 2020-10-25
243004361 2020-10-26
248233045 2020-10-27 
select
  avg(a.daily_streams) avg_daily_streams,
  format_date('%m - %b',day) month,
  format_date('%w %A',day) day_of_week
from a
group by day_of_week, month

heatmap