Month: July 2020

Frequencies

~ chriseyre2000 ~ Leave a comment

This is a simple powershell script that can be used to get the frequency of the first letter from a sample file.

gc ‘./sample’ | %{ $_.substring(0,1) } | group

Running this over say the FTSE 100 symbol list returns:

Count Name                      Group
----- ----                      -----
   10 A                         {A, A, A, A...}
   11 B                         {B, B, B, B...}
    4 C                         {C, C, C, C}
    2 D                         {D, D}
    2 E                         {E, E}
    3 F                         {F, F, F}
    3 G                         {G, G, G}
    5 H                         {H, H, H, H...}
    8 I                         {I, I, I, I...}
    3 J                         {J, J, J}
    1 K                         {K}
    4 L                         {L, L, L, L}
    4 M                         {M, M, M, M}
    3 N                         {N, N, N}
    1 O                         {O}
    6 P                         {P, P, P, P...}
    8 R                         {R, R, R, R...}
   15 S                         {S, S, S, S...}
    2 T                         {T, T}
    2 U                         {U, U}
    1 V                         {V}
    2 W                         {W, W}

This highlights that the symbols are not uniformly spread across the alphabet.

A-F has 1/3 of the market as does P-Z

I found out this once when trying to use the ticker symbol to load balance market data across 3 servers.

Check the distribution of the data before you use a simple key.

Oddly the second letter is a better key:

    6 A                         {A, A, A, A...}
    3 B                         {B, B, B}
    4 C                         {C, C, C, C}
    5 D                         {D, D, D, D...}
    3 E                         {E, E, E}
    6 G                         {G, G, G, G...}
    4 H                         {H, H, H, H}
    3 I                         {I, I, I}
    2 K                         {K, K}
    8 L                         {L, L, L, L...}
    6 M                         {M, M, M, M...}
    7 N                         {N, N, N, N...}
    2 O                         {O, O}
    4 P                         {P, P, P, P}
    8 R                         {R, R, R, R...}
    9 S                         {S, S, S, S...}
    7 T                         {T, T, T, T...}
    2 U                         {U, U}
    6 V                         {V, V, V, V...}
    2 W                         {W, W}
    2 X                         {X, X}
    1 Z                         {Z}

Elixir Demo

~ chriseyre2000 ~ Leave a comment

This video really demonstrates the power of Elixir: https://t.co/dXljW61NYt?amp=1

Here is the source code for this:

https://github.com/sasa1977/demo_system

It requires a really old version of node (8.3.0).

The demo mostly works with the latest version of Elixir. One of the buttons to set the number of processes does not work, however calling the function in the iex session does work.

I managed to get 10k processes running on a MacBook.

Using Typescript for an NPM Module

~ chriseyre2000 ~ Leave a comment

This is a useful article on building an NPM Module using typescript.

I am using the technique here to move lie.js to typescript.

The documentation is now a little old. Have a look at github.com/chriseyre2000/lie.js for a more recent version.

The practical advantage of moving to Typescript are the type definitions which the IDE can choose to use even if the module is used from a Javascript app.

Also note that I have CircleCI setup to publish to NPM upon receipt of a tag.

This is how to push tags to github:

git tag -a v1.1.4 -m "my version 1.1.4"
git push origin --tags