javascript - taking one element of each type from a list and only taking the first occurrence not working as expected

Question

So this function is supposed to pars an array of object and only take the first occurrence of each type of object there is like 4 different ones and each ones has a dozen of entries.

    LastReadingOfEach(measurements){
        let devicesList = []
        devicesList.push(measurements.map((device) => {if (!devicesList.includes(device.Type) ) { return device} else console.log("removed :")}))
        console.log("devicesList : ", devicesList)
    }

I created an array and thought I could just push in a device of each type, but I think it doesn't compare against the array as it fill up because it at the end I find the devicesList has all elements on measurements

question from:https://stackoverflow.com/questions/66054866/taking-one-element-of-each-type-from-a-list-and-only-taking-the-first-occurrence

Answer 1

I believe what you're looking for can be done with a reducer and findIndex. If find index fails to match the device type it will return -1, we know that we don't have that type yet so it gets pushed into the aggregation.

    LastReadingOfEach(measurements){
        const devicesList = measurements.reduce((agg, device) => {
          if (agg.findIndex(x => x.type === device.type) === -1) { 
            agg.push(device)
          } 
          return agg
        }, [])
        console.log("devicesList : ", devicesList)
    }