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javascriptarrays
Tony Bai
Tony Bai

Reputation: 396

javascript - How to check if array has at least one negative value?

I created an array of integers and wanted to know if it had one or more negative values in it.

I do not want to create a for() loop and check if each element in the array is positive or negative because I only want to return once (ex: I don't want my function to "return false;" a million times).

One option I considered was multiplying each value in the array by the absolute value of its reciprocal, so I get an array of 1s or -1s (or undefined if value is 0) and then I could sum all of the values in this second array to see if it equals the length of the array.

However, the problem with this method is it does not account for 1/0, and also it is tedious. I want to know if there is a faster way to check if an array contains at least one negative value.

--from a beginner JavaScript programmer

Upvotes: 8

Views: 22682

Answers (4)

Thomas Maddocks
Thomas Maddocks

Reputation: 1385

You could leverage Array.prototype.some which will return true or false if an item in the array matches the given condition. It'll also stop checking remaining values if the condition matches an element:

let values = [1, 4, 6, -10, -83];
let hasNegative = values.some(v => v < 0);

Upvotes: 21

Cavan Page
Cavan Page

Reputation: 535

This will only return 1 value and break as soon as a negative is found. 

function doesArrayContainNegative(array){

  //if negative is found return true (breaking loop)
  for(var arr of array){
  	if(arr < 0) return true;
  }
  
 //if no elements are negative return false
  return false;
}

var array1 = [9, -3, 5, 8]
console.log(doesArrayContainNegative(array1))

Upvotes: 1

Derek Lawrence
Derek Lawrence

Reputation: 1608

What's the issue with the for loop needing to return false all the time?

fucntion containsNegative(myArray)
    for(var i = 0; i < myArray.length(); i++)
    {
        if(myArray[i] < 0){
            return true;
        }
    }
    return false;
}

and if you wanted to get the amount of negative numbers

fucntion getNegative(myArray)
    var count = 0;
    for(var i = 0; i < myArray.length(); i++)
    {
        if(myArray[i] < 0){
            count++
        }
    }
    return count;
}

Upvotes: 0

MDA
MDA

Reputation: 113

why do you find min value in array? see

JavaScript: min & max Array values?

Math.min(...array)

Upvotes: 2

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