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Transpose Array of Objects to Object of Arrays
cities = FileAttachment("cities.json").json()
properties = ["cost", "internetSpeed"]
propArray = curry(
(prop, list) =>
({
[prop]: map(k => k[prop], list)
})
)
costs = propArray("cost")
cityCostsObject = costs(cities)
cityCosts = cityCostsObject.cost
cityCostAverage = sum(cityCosts) / length(cityCosts)
transpose = curry((properties, list) => reduce(
(collector, item) =>
({
...collector,
...propArray(item)(list)
}),
{}
)(properties))
extractor = transpose(properties)
extractor(cities)
transposePusher = ((collector, item) => {
const { cost = [], internetSpeed = [] } = collector // initialize the collector with two empty arrays
return merge(
collector,
{
cost: append(item.cost, cost),
internetSpeed: append(item.internetSpeed, internetSpeed)
}
)
})
groupedByProp = reduce(transposePusher, {}, cities)
times = 1e5 // NOTA BENE: setting times to more than 1e5 may stall your browser tab/window; take care!
{
if (false) { // set to true if you want to do a timing test (times appear in the console)
console.time()
for (let i = 0; i < times; i++) transpose(properties, cities)
console.timeEnd()
return transpose(properties, cities)
}
}
{
if (false) { // set to true if you want to do a timing test (times appear in the console)
console.time()
for (let i = 0; i < 1e4; i++) reduce(transposePusher, {}, cities)
console.timeEnd()
return reduce(transposePusher, {}, cities)
}
}
Purpose-built for displays of data
Observable is your go-to platform for exploring data and creating expressive data visualizations. Use reactive JavaScript notebooks for prototyping and a collaborative canvas for visual data exploration and dashboard creation.
