Sort documents by date and group by type - mapreduce

Question

I don't know how to write map/reduce functions to get all film genres sorted by date of the latest film.
async function test() {
const db = new PouchDB("film")
const docs = [
{ _id: "1", title: "Rambo", year: 2008, genre: "Action" },
{ _id: "2", title: "Forrest Gump", year: 1994, genre: "Drama" },
{ _id: "3", title: "Gladiator", year: 2000, genre: "Action" },
{ _id: "4", title: "The Mask", year: 1994, genre: "Comedy" }
]
await db.bulkDocs(docs)
const fan = {
map(doc) {
emit([doc.year, doc.genre])
},
reduce(keys, values, rereduce) {
return values
}
}
const result = await db.query(fan, { group: true })
result.rows.forEach(r => console.log(r))
}
Returns:
{key: [1994, "Comedy"], value: [null]}
{key: [1994, "Drama"], value: [null]}
{key: [2000, "Action"], value: [null]}
{key: [2008, "Action"], value: [null]}

Answer 1

I would probably invert the order of the fields indexed.
Here's some examples:
async function test() {
const db = new PouchDB("film");
const docs = [
{ _id: "1", title: "Rambo", year: 2008, genre: "Action" },
{ _id: "2", title: "Forrest Gump", year: 1994, genre: "Drama" },
{ _id: "3", title: "Gladiator", year: 2000, genre: "Action" },
{ _id: "4", title: "The Mask", year: 1994, genre: "Comedy" }
];
await db.bulkDocs(docs);
const fan = {
map: function(doc) {
emit([doc.genre, doc.year])
},
reduce: '_count'
};
// Get the view output
const result = await db.query(fan, {
reduce: false,
include_docs: true
})
// Get a certain group
const actionFilms = await db.query(fan, {
startkey: ["Action"],
endkey: ["Action", {}],
reduce: false,
include_docs: true
});
// Get the list of groups
const genres = await db.query(fan, {
group: true,
group_level: 1
});
// Get the most recent value of a group
const lastActionFilm = await db.query(fan, {
startkey: ["Action", {}],
endkey: ["Action"],
reduce: false,
descending: true,
limit: 1,
include_docs: true
});
result.rows.forEach(r => console.log(r))
}