Grab a data file. "American movies scraped from Wikipedia" is a nice condence set at size 3.4M
wget https://raw.githubusercontent.com/prust/wikipedia-movie-data/master/movies.json -O movies.json
Slice movies made from 1920 till 1930 and output them line by line
jq -cr '.[] | select(.year >= 1920 and .year <= 1930)' movies.json
Pass the output to reducer to group by year, calculate total movies per year and accumulate movies into "movies" array in each block