Function to iterate through an array of maps to return the lowest value associated with a specific key

Question

I am trying to write a function that accepts an array of maps and a key and returns the minimum value associated with the given key. For example,

minKeyVal([{ a: 1, b: 4 }, { a: 2, b: 6 }, { a: 3, b: 1 }], 'b'); //should return 1.

I can get this to work outside of a function as follows:

//sample array of maps
const originalArray = [
  { a: 1, b: 4 },
  { a: 2, b: 6 },
  { a: 3, b: 1 },
];
 
//select values by a specific key
const newArray = originalArray.map(object => object.b);

//in the new array of B values, iterate through to find the min
var res = newArray[0];
for(let i = 1; i < newArray.length; i++) {
  if(newArray[i] < res){
      res = newArray[i]
  }
}

//print result
console.log(res);

// 1 is returned

When I have attempted to create a function based on this logic, I have not been successful. This is my latest attempt, which returns undefined:

function minKeyVal (originalArray, id) {
  const newArray = originalArray.map(object => object.id);

  var res = newArray[0];
  for(let i = 1; i < newArray.length; i++) {
    if(newArray[i] < res){
        res = newArray[i]
    }
    return res;
  }
}
console.log(minKeyVal([
    { a: 1, b: 4 },
    { a: 2, b: 6 },
    { a: 3, b: 1 },
  ], 'b'));

Help, hints and suggestions all welcome! I'd actually prefer suggestions of what to try or resources that might guide me so I can continue to work through it :)

`originalArray.map(object => object.id)` should have `object[id]` — blex, Dec 17 '20 at 22:31
function minKeyVal(list, char) { return Math.min(...list.map(x => x[char])) } — EugenSunic, Dec 17 '20 at 22:32
Thanks all - these answers, tips and the info are all quite helpful. Most appreciated. — J. Fede, Dec 18 '20 at 11:34

score 3 · Answer 1 · answered Dec 17 '20 at 22:32

3

You could map an array with the wanted key and get the minimum of it.

const
    minKeyVal = (array, key) => Math.min(...array.map(o => o[key]));

console.log(minKeyVal([{ a: 1, b: 4 }, { a: 2, b: 6 }, { a: 3, b: 1 }], 'b'));

answered Dec 17 '20 at 22:32

Nina Scholz

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Ori Drori · Answer 2 · 2020-12-17T22:36:52.610

1

Use Array.reduce() to convert an array to a single value:

const minKeyVal = (originalArray, id) => 
  originalArray.reduce((acc, item) => acc < item[id] ? acc : item[id], Infinity)
  
const result = minKeyVal([{"a":1,"b":4},{"a":2,"b":6},{"a":3,"b":1}], 'b')

console.log(result);

edited Dec 17 '20 at 22:36

answered Dec 17 '20 at 22:32

Ori Drori

183,571
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score 0 · Accepted Answer · answered Dec 17 '20 at 22:34

It's because you always look up the 'id' property (literally) because of the . accessor syntax, and not the property named the value of the id variable.

Change it into a dynamic key lookup ([] accessor syntax):

function minKeyVal (originalArray, id) {
  const newArray = originalArray.map(object => object[id]);

  var res = newArray[0];
  for(let i = 1; i < newArray.length; i++) {
    if(newArray[i] < res){
        res = newArray[i]
    }
    return res;
  }
}

Function to iterate through an array of maps to return the lowest value associated with a specific key

3 Answers3