Essays/Coin Flipping

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What is your chance to get 3 heads in a row from ten coin flips?

There was an original blog post to answer that question with Monte Carlo simulation in Python. How can we do that in J?


Random Coin Flips

Let's say 1 signifies head and 0 tail. Then we could easily roll a sequence of coin flipping as:

   ?.30$ 2
0 1 0 1 1 1 0 0 0 1 0 1 0 0 1 0 0 0 0 0 1 1 1 0 0 0 0 0 1 1

Counting consecutive heads

How do we count number of consecutive heads?

    (* >:)/\.&.|. ?.30$2
0 1 0 1 2 3 0 0 0 1 0 1 0 0 1 0 0 0 0 0 1 2 3 0 0 0 0 0 1 2

Notice the usage of /\.&.|., which is a common phrase in J to do operations accumulatively.

Maximal number of consecutive heads

It's easy at this stage.

    >./ (* >:)/\.&.|. ?.30$2
3

Were there 3 heads in a row?

    3<: >./ (* >:)/\.&.|. ?.30$2
1

Monte Carlo

How can we easily move what we've done to a multiple of experiments, that is Monte Carlo simulations?

    i%~ +/ 3<: ([:>./(* >:)/\.&.|.)"1 ?.((i=.1000000), 10)$2
0.508196

Notice the rank("1) applied to the previous expression to make it applied each row.


Originally written by June Kim. Variations and suggestions are welcome.