Can somebody please explain the concept of Event Indexing?

Question

Here is what the doc says:

Up to three parameters can receive the attribute indexed which will cause the respective arguments to be searched for: It is possible to filter for specific values of indexed arguments in the user interface.

OK, so I understand that I can define an event, for example, with three indexed parameters:

event Event(address indexed from, address indexed to, uint indexed id, uint value);

But what exactly is the benefit of using that indexed keyword?

Up until now, I've been defining events with no indexing, for example:

event Event(uint value);

Then, on the web3-client side, I retrieve the value of the event as follows:

let hash = await myContract.myFunc(...);
let data = web3.toBigNumber(hash.receipt.logs[0].data);

If I know that several events are emitted during the execution on the blockchain side, then instead of 0, I use the index of the specific event which I want to retrieve.

So I'm guessing that perhaps this indexed keyword can be used in order to retrieve events on the client side in a cleaner manner.

Am I right, and if yes, how exactly would I retrieve an indexed event on the client side differently than how I am retrieving it at present?

Thank you.

Answer 1

Indexing can be used for filtering the events for specific values.

 var myEvent = contract.Event({from:"0xc32c36e7cea09c00e0dbd4bb4e72b8baaa51fd45"},{fromBlock: 0, toBlock: 'latest'});
    myEvent.get((error, result) => {
                     console.log(result);
    });

Here I am filtering the events based on the from param having a specific value(0xc32c36e7cea09c00e0dbd4bb4e72b8baaa51fd45). It will return the event logs for the particular address instead of all event logs.