Learning R

funkysi1701@gmail.com (funkysi1701) — Mon, 27 Feb 2017 20:00:45 +0000

Today I spent some time learning the R language.

The problem I was trying to solve was to convert local prices of some items into Euros. I had been using a fixed exchange rate for all data, but as exchange rates fluctuate so much this is incorrect.

My first though was to find a free API that I could query to get the values I wanted. The first API I found didn’t cover all the currencies, the next one I found I burnt through the free allowance in one pass.

A colleague of mine mentioned using R to solve this, he sent me some links and I set out to write my first piece of R code.

My finished code can be found on github and I will attempt to explain some of it.

R defines functions fairly simply

nameoffunction <- function(arg1, arg2)
{
 arg1 * arg2
}

I have created a function that takes 2 parameters date and currency. I know I have about 10 different currencies that I want to get currencies for and I want to loop through each day so I will need to pass in a date.

The source of my exchange rate information is the www.xe.com website, its historical exchange rate page passes currency and date into the query string so I should be able to build up a string containing all the different elements.

All programming language can concatenate strings and R is no different. R uses paste()

var <- paste("Hello", "World")

However R has an annoying feature in this function. I would expect that var in the above example would contain “HelloWorld”, it doesn’t it contains “Hello World”. Why it automatically adds a space I don’t know?

var <- paste("Hello", "World", sep="")

I am not entirely sure what all of the code does but I can take a good guess.

read_html() I would guess loads a html page, html_nodes() finds all the html tags of a certain type on the page, in my case <table>, html_table() reads the first table it finds.

table1[2] selects the second column, and head() selects a specific number of rows. I want the first row and second column so I combine these two as head(table1[2],1)

Now that I have found my exchange rate what do I do with it? R can read and write to SQL Server so why not store this info in a SQL lookup table. I can then use this data in a stored procedure when I process my data.

To query sql you can use sqlQuery(), it has two parameters, a sql connection and a TSQL command (eg a SELECT, INSERT, UPDATE statement)

I use a while loop to loop through every day between 1st October 2016 and today and look up the exchange rate for each currency.

For now I am manually running this R script, however there are ways to run R directly from SQL Server which I may well investigate. I could then have a SQL job to run this on a schedule, maybe once a day to get the latest exchange rates. I also would like to do something a bit cleverer like only getting exchange rates for the days that I need them by querying existing database tables.

Side Project – Connect 4

funkysi1701@gmail.com (funkysi1701) — Mon, 06 Feb 2017 20:00:45 +0000

Hello?

You have probably like me almost forgotten about this blog. Life has got in the way over the last few months, but lets see if I can restart my blogging habit.

In 2017 I want to start a side project for a few reasons. I want to improve my coding skills and look at things I wouldn’t normally during my day job.

I have been trying to decide what to build. The actual project doesn’t matter too much, it is the techniques I use during build that matters the most. I would like something that I can start off as a windows app and then extend onto the web or mobile apps.

I started off thinking about a Rubik’s cube app, however my initial coding has lead me to believe it is probably too complex for my first app.

Last year I spent an evening looking at Connect 4 during a York Code Dojo session. I think this should be complex enough that I can code some logic to efficiently solve the game, however not too complex I get defeated before building too much.

So far I have built a console app that displays via Console.Write() commands, a grid to represent the game, with 0 meaning empty, 1 red and 2 yellow etc. I am currently working on the logic to solve the game, once I have that in a good state I can extend into a winforms app, into a web (MVC most likely) app and finally a mobile app (I have no knowledge about how to do this yet, but something I would like to try one day).

Over the last few days I listened to .NetRocks where they discussed Progressive Web Apps . This sounds like a great challenge for me to aim for. A progressive Web App is a website that automatically detects various properties to give you an app that runs well whatever the state of your internet connection and whatever browser you are in.

I have lots to learn but I can split it down into small sections and I can build something that demonstrates some of my skills.

2017-02 on Funky Si's Test

Learning R

Side Project – Connect 4