How to counter Swain
Let us take a look on how to beat Swain. We will look at champions who are strong against Swain and who are weak against Swain. Use win rate, gold difference and creep score difference at minute 10 to find the best 
Adc champion who counters Swain. You can already win in champion select with the right counters for Swain. If you want to know how to counter Swain then you need to take into account the best picks vs Swain and the worst picks vs Swain. This Swain counter data is based on matches played by Pros on patch 13.24 and previous ones. It is important to see whether Pros counter picked Swain or whether they played as Swain.
Champions used by Pros to counter pick Swain
Looking at the matches from Pros (see table Pros counter picked Swain) we can see that they picked 
Ezreal most often to counter pick Swain. The matchup Ezreal vs Swain occured 6 times. Swain has 4 wins and 2 losses in this matchup. Learn how to counter pick Ezreal to get another perspective on the data.
Lane outcome for Swain
When looking at Swain counters you will notice that win rates alone are not conclusional. Therefore we provide an overview (see table Lane Outcome) where you can see the lane outcome of Pros who played Swain. The lane outcome of Swain consists of three outcomes: Win, Loss or Draw. Let's take a look of Swain lane and match outcome for specific matchups. Considering the lane outcome and the match outcome of a specific matchup, might enable you to find the right counter for Swain.
Conclusion
Analyze the available data and learn how to beat Swain. To master Swain take also a look on Swain builds and runes for Swain. Good luck, Summoner!