A real-time map of NYC Citi Bike stations colored by the number of bikes available at each updating once per second. A full blog post can be found here.
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July 29, 2020 04:52
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Perspective NYC Citibike Example
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| license: apache-2.0 | |
| height: 1200 |
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| // Quick wrapper function for making a GET call. | |
| function get(url) { | |
| return new Promise(resolve => { | |
| const xhr = new XMLHttpRequest(); | |
| xhr.open("GET", url, true); | |
| xhr.responseType = "json"; | |
| xhr.onload = () => resolve(xhr.response); | |
| xhr.send(null); | |
| }); | |
| } | |
| // Fetch feed data from NYC Citibike, if a callback is provided do it again every 1s asynchronously. | |
| async function get_feed(feedname, callback) { | |
| const url = `https://gbfs.citibikenyc.com/gbfs/en/${feedname}.json`; | |
| const {data: {stations}, ttl} = await get(url); | |
| if (typeof callback === "function") { | |
| callback(stations); | |
| setTimeout(() => get_feed(feedname, callback), ttl * 1000); | |
| } else { | |
| return stations; | |
| } | |
| } | |
| // Create a new Perspective WebWorker instance. | |
| const worker = perspective.worker(); | |
| // Use Perspective WebWorker's table to infer the feed's schema. | |
| async function get_schema(feed) { | |
| const table = worker.table(feed); | |
| const schema = await table.schema(); | |
| table.delete(); | |
| return schema; | |
| } | |
| // Create a superset of the schemas defined by the feeds. | |
| async function merge_schemas(feeds) { | |
| const schemas = await Promise.all(feeds.map(get_schema)); | |
| return Object.assign({}, ...schemas); | |
| } | |
| async function main() { | |
| const feednames = ["station_status", "station_information"]; | |
| const feeds = await Promise.all(feednames.map(get_feed)); | |
| const schema = await merge_schemas(feeds); | |
| // Creating a table by joining feeds with an index | |
| const table = worker.table(schema, {index: "station_id"}); | |
| // Load the `table` in the `<perspective-viewer>` DOM reference with the initial `feeds`. | |
| for (let feed of feeds) { | |
| table.update(feed); | |
| } | |
| // Start a recurring asyn call to `get_feed` and update the `table` with the response. | |
| get_feed("station_status", table.update); | |
| // Get `<perspective-viewer> elements from the DOM. | |
| const viewers = document.getElementsByTagName("perspective-viewer"); | |
| // Load the `table` for each `<perspective-viewer>` DOM reference. | |
| for (viewer of viewers) { | |
| viewer.load(table); | |
| } | |
| } | |
| main(); |
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| #grid { | |
| display: flex; | |
| max-width: 600px; | |
| max-height: 1200px; | |
| margin: auto; | |
| flex-direction: column; | |
| } | |
| #grid perspective-viewer { | |
| height: 600px; | |
| width: 600px; | |
| flex: 1; | |
| display: block; | |
| } |
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| <!DOCTYPE html> | |
| <html> | |
| <head> | |
| <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, minimum-scale=1, user-scalable=no"> | |
| <script src="https://unpkg.com/@finos/perspective/build/perspective.js"></script> | |
| <script src="https://unpkg.com/@finos/perspective-viewer/build/perspective.view.js"></script> | |
| <script src="https://unpkg.com/@finos/perspective-viewer-hypergrid/build/hypergrid.plugin.js"></script> | |
| <script src="https://unpkg.com/@finos/perspective-viewer-d3fc/build/d3fc.plugin.js"></script> | |
| <script src="citibike.js"></script> | |
| <link rel='stylesheet' href="https://unpkg.com/@finos/perspective-viewer/build/material.css" is="custom-style"> | |
| <link rel='stylesheet' href="index.css"> | |
| </head> | |
| <body> | |
| <div id="grid"> | |
| <perspective-viewer | |
| row-pivots='["name"]' | |
| columns='["num_bikes_available"]' | |
| sort='[["num_bikes_available","desc"]]'> | |
| </perspective-viewer> | |
| <perspective-viewer | |
| view='d3_xy_scatter' | |
| row-pivots='["name"]' | |
| columns='["lon","lat","num_bikes_available"]' | |
| sort='[["num_bikes_available","asc"]]'> | |
| </perspective-viewer> | |
| </div> | |
| </body> | |
| </html> |
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