How can I type the reduce function parameters.
interface IGroupArrayByKey<T> {
data: T[]
key: string
}
export const groupArrayByKey = <T>({ data, key }: IGroupArrayByKey<T>): object => {
return data.reduce((acc: any, item: any) => {
return { ...acc, [item[key]]: [...(acc[item[key]] || []), item] }
}, {})
}
groupArrayByKey function works on the principle that you provide the array as a date and key which the array should be grouped
Couple of notes:
keyof T lists all properties of type T and doesn't allow passing arbitrary string that is not a key of the object there. Very useful imho.item[keyProp] is a string, but indexer in an object could only be a string or a number. That's why this ugly as unknown as string. If you would have used a Map, then we wouldn't need the cast.interface IGroupArrayByKey<T> {
data: T[]
keyProp: keyof T
}
export const groupArrayByKey = <T>({ data, keyProp }: IGroupArrayByKey<T>) => {
return data.reduce<{ [key: string]: T[] }>((acc, item) => {
const key = item[keyProp] as unknown as string;
return { ...acc, [key]: [...(acc[key] || []), item] }
}, {})
}
