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11.6 Recursively concatenate field values

 
spl-cookbook(224)

The following JSON file records numbers of confirmed cases of COVID-19 in different regions of the world at a certain time, and we want to find the total number worldwide. Below is part of the JSON file:

[
    {Region:"USA",Confirmed:[
        {Region:"California",Confirmed:3671902},
        {Region:"New York",Confirmed:1139740},
        {Region:"Virginia",Confirmed:620801},
        {Region:"Florida",Confirmed:2064525},
        …
    ]},
    {Region:"Brazil",Confirmed:[…]},
    {Region:"India",Confirmed: […]},
    {Region:"France",Confirmed: […]}
    …
]

Some countries have the country-level numbers, some have state/province-level numbers and some offer city-level numbers. In this case we cannot loop through field values and simply sum them. Instead, we need recursive sum. SPL has A.conj@r() function to concatenate members of sequences recursively.

SPL script:

A
1 =json(file(“COVID-19.json”).read())
2 =A1.field@r(“Confirmed”)
3 =A2.conj@r().sum()

A1 Import the JSON file.
A2 Use A.field@r() function to get all Confirmed field values recursively.
A3 Use A.conj@r() function to concatenate all confirmed cases and perform sum.

spl-cookbook(224)
 
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