This is how my array looks like:
["Car","model","year","color","price"]
["Table","model","year","color","price"]
["Car","model","year","color","price"]
["Car","model","year","color","price"]
["Laptop","model","year","color","price"]
["Laptop","model","year","color","price"]
now I want to group by this in typescript and count how many of that item exist in array (also like in sql)
name |count
Car | 3
Laptop| 2
Table | 1
and in my typescript file I have this
private groupByObjects() {
//this read all data in array allData[] from service
this.dataService.retrieveData().subscribe(allData => {
});
}
Could anyone please help me to write this in typescript?
CodePudding user response：
You can do this is O(n) through a simple reduction
In your case,
type 2DArray<T = string> = Array<Array<T>>
const groupAndApplyByIndex<T, R>(data: 2DArray<T>, index: number, apply: (element?: T) => R): Record<string, R> => {
return data.reduce((counts, element) => (
...counts,
[element[index]]: apply(element[index])
}), {})
}
And just use the above funtion in your code by:
private groupByObjects() {
//this read all data in array allData[] from service
this.dataService.retrieveData().subscribe(allData => {
counts = groupAndCountByIndex(allData, 0, (element) => (element || 0) 1))
// Rest of your logic...
});
By using the above method, you have a function which can count or do other transformations that you define through apply
CodePudding user response：
I like the approach of a list reducer using a function that return another function. That way you can always specify which key to use, in your case this key is 0.
interface PropObject {
[index: string]: number;
}
const groupByCounter = (key : number) => (result : PropObject ,current : string []) => {
const item = Object.assign({},current);
if (typeof result[current[key]] == 'undefined'){
result[current[key]] = 1;
}else{
result[current[key]] ;
}
return result;
};
const data : string [][] = [["Car","model","year","color","price"],
["Table","model","year","color","price"],
["Car","model","year","color","price"],
["Car","model","year","color","price"],
["Laptop","model","year","color","price"],
["Laptop","model","year","color","price"]];
const group = data.reduce(groupByCounter(0),{});
console.log(group);