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Naive JS implementation of tidyr's gather function. Intended for use with JSON-styled tabular data... like you'd get from d3.dsv
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function withFields<S>(record: S, fields: (keyof S)[]) { | |
// Returns record with only properties specified in fields | |
return fields.reduce((acc: Partial<S>, key) => { | |
acc[key] = record[key] | |
return acc | |
}, {}) | |
} | |
function splitRecord<S extends object>(record: S, ...fields: Array<keyof S>) { | |
let withGivenFields = withFields(record, fields) | |
let otherFields = keys(record).filter((key: keyof S) => !fields.includes(key)) | |
let withOtherFields = withFields(record, otherFields) | |
return [withOtherFields, withGivenFields] | |
} | |
function keys<O extends object>(obj: O): Array<keyof O> { | |
return Object.keys(obj) as Array<keyof O> | |
} | |
function lengthen<S extends object>(record: Partial<S>, keyLabel: string, valueLabel: string) { | |
return keys(record).map(key => ({ [keyLabel]: key, [valueLabel]: record[key] })) | |
} | |
export function gather<S extends object = object>( | |
data: S[], | |
keyLabel: string, | |
valueLabel: string, | |
...columns: (keyof S)[] | |
) { | |
let result: any | |
return data | |
.map(record => { | |
let [keptFields, wideFields] = splitRecord(record, ...columns) | |
let longFields = lengthen<S>(keptFields, keyLabel, valueLabel) | |
let nestedArrays = longFields.map(longField => Object.assign({}, wideFields, longField)) | |
return nestedArrays | |
}) | |
.reduce((acc, arr) => acc.concat(arr), []) | |
} |
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