How to get unique items from an array

• notes • javascript

Challenge

I had a very basic problem recently wherein I had to make a form for data with a dynamic unique enum attribute say “type of business”, “club affiliation” or something similar. Data from the API is directly provided in the form and this field, a dropdown, had to be always updated with the latest pool of values.

Basically there is an array of repeated values and we need an array of unique values from the first.

Solution

I have two solutions that arrive to the same result.

Here is a sample data that mirrors what my original data looked like:

const data = [
    {
        "industry": "Law",
        "id": 62683781,
    },
    {
        "industry": "Telecommunications",
        "id": 73385749,
    },
    {
        "industry": "Law",
        "id": 22759989,
    },
    {
        "industry": "Health Services",
        "id": 15438299,
    },
    {
        "industry": "Education",
        "id": 62683781,
    },
  ...
]

and the expected array should contain the following:

["Law", "Telecommunications", "Health Services", "Education", ...]

Array manipulation

I just made a new array from a set generated from the industry attributes. The set is a powerful tool here as it creates and stores unique values from the inputs.

const result = Array.from(
    new Set(
      data.map(item => item.industry)
    )
  )

for-loop

I also wanted to make sure to find another simple way that uses tried-and-tested basic JavaScript tools such as loops.

This solution just maintains an array to insert unique values determined by indexOf. If the value is not found in results, that means it is not yet found and should return -1.

There exists a similar method includes() that returns a boolean but the difference is that this one returns true for the NaN value which is unpredictable hence the decision to use the first.

const results: string[] = []
for(let i = 0; i < data.length; i++) {
  if(results.indexOf(data[i].industry) === -1) {
    results.push(data[i].industry)
  }
}

References

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