Request and compare API Reponses in Oraclize call

Question

I want to send requests to 3 Weather APIs and compare their results like if the rainfall at a specific day were the same London to avoid the single point of failure.

I already learned how I can send multiple requests to APIs. What is the best way to compare their results in Solidity? Is there already a mechanism from oraclize itself?

Answer 1

Comparing the results of an API call will be the same as comparing any other data in Solidity.

In your example, you are comparing weather, which is likely a uint256. You will likely also need the date you are comparing, which would be a timestamp (also a uint256). Each of these data sources would need a mapping of timestamp to temperature. The mappings would look as follows:

mapping (uint256 => uint256) public sourceOneWeather;
mapping (uint256 => uint256) public sourceTwoWeather;
mapping (uint256 => uint256) public sourceThreeWeather;

Comparing them would simply be to put them into a conditional statement and returning the output of whatever comparison you desire.

Add function example, per comments

An example comparison function would be:

function compareResults(uint256 _timestamp) public returns (uint256){
    if (sourceOneWeather[_timestamp] > sourceTwoWeather[_timestamp]):
        if (sourceOneWeather[_timestamp] > sourceThreeWeather[_timestamp]):
            return sourceOneWeather[_timestamp];
        else:
            return sourceThreeWeather[_timestamp];
    else if (sourceTwoWeather[_timestamp] > sourceThreeWeather[_timestamp]):
        return sourceTwoWeather[_timestamp];
    return sourceThreeWeather[_timestamp];