Caching

Let's suppose that the 'home prices' dataset is not exactly what we are looking for, we can try to search online for 'home prices' and find out that catalog.data.gov contains a more suitable FHFA House Price Indexes dataset. Instead of giving users explicit instructions to download the CSV file, we can instead use pin() to cache this dataset locally:

JavaScript
Python

 pins.pin("http://www.fhfa.gov/datatools/downloads/documents/hpi/hpi_master.csv",
          { name: "home_price_indexes" })

Notice that the pin returns a path to a local CSV file, which you are free to load with your favorite package.

JavaScript
Python

 var data = pins.pin("http://www.fhfa.gov/datatools/downloads/documents/hpi/hpi_master.csv",
          { name: "home_price_indexes" })
 d3.csvParse(data)

The pins.js library makes use of HTTP headers like cache-control and ETag to avoid downloading files when they have not changed or when the cache has not expired.