npm linq：分组多列

Question

I am trying to group by 2 columns in an array of objects and get a grouped sum total of a value. i have been using linq for this and this is the code:

import Enumerate from "linq";

let data = [ 
{ Phase: "Phase 1", Step: "Step 1", Task: "Task 1", Value: "5" },
{ Phase: "Phase 1", Step: "Step 1", Task: "Task 2", Value: "10" },
{ Phase: "Phase 1", Step: "Step 2", Task: "Task 1", Value: "15" },
{ Phase: "Phase 1", Step: "Step 2", Task: "Task 2", Value: "20" },
{ Phase: "Phase 2", Step: "Step 1", Task: "Task 1", Value: "25" },
{ Phase: "Phase 2", Step: "Step 1", Task: "Task 2", Value: "30" },
{ Phase: "Phase 2", Step: "Step 2", Task: "Task 1", Value: "35" },
{ Phase: "Phase 2", Step: "Step 2", Task: "Task 2", Value: "40" }
];

var result = Enumerate.from(data)
.groupBy((x) => x.Phase + ':'+ x.Task)
.select((x) => {
  return {
    Phase: x.first().Phase,
    Task: x.first().Task,
    Value: x.sum((y)=> y.Value | 0)
  };
})
.toArray();

console.log (result);

and I get the expected result:

Array(4)[
0: Object { Phase: "Phase 1" ,Task: "Task 1" ,Value: 20 }
1: Object { Phase: "Phase 1" ,Task: "Task 2" ,Value: 30 }
2: Object { Phase: "Phase 2" ,Task: "Task 1" ,Value: 60 }
3: Object { Phase: "Phase 2" ,Task: "Task 2" ,Value: 70 }
length: 4
]

I struggled a bit to come to this result and had to use some workarounds like a string key in the groupBy and x.first() when selecting the data. My question is, is this the proper way to do it? Or am I missing something?

Answer 1

I'm not experienced with linq.js, but I'll give some insights based on my C# experience and what I can glean from the documentation.

It looks like there are additional arguments you can provide to the groupBy function to make this more elegant. The arguments are:

1. the key selector
2. the value selector
3. a selector that merges the key and values into the desired output per group
4. a compare selector to produce a comparable value from the key produced in #1

So I think something like this should work:

var result = Enumerate.from(data)
.groupBy((x) => ({Phase: x.Phase, Task: x.Task}),
         (x) => x.Value | 0,
         (key, values) => ({
             Phase: key.Phase,
             Task: key.Task,
             Value: values.sum()
         }),
         (key) => key.Phase + ':'+ key.Task)
)
.toArray();