Using Amazon DynamoDb for IP and co-ordinate based geo-location services part 2: MaxMind source files

April 12, 2015 2 Comments

Introduction

In the previous post we outlined the goals of this series and the tools that we’re going to use. We’ve got as far as downloading MaxMind’s free version of their geo-location source with IPs and longitude-latitude co-ordinates. We saw that the downloaded package had a number of CSV files.

In this post we’ll start off by looking at the structure of those files and how they are connected.

The source files

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Using Amazon DynamoDb for IP and co-ordinate based geo-location services part 1: introduction and goals

April 11, 2015 1 Comment

Introduction

There are a lot of applications out there that involve finding a point on a map. Putting hotels, restaurants, metro stations etc. on a map on your mobile device has become commonplace. Queries that find the nearest hospital, theatre or school need to be executed in a fast and efficient manner.

In this series we’ll discuss a possible solution to the following geo-location related scenarios:

  • You have a pair of longitude (lng) and latitude (lat) co-ordinates and you’d like to find all locations in a circle around that point or just the nearest relevant location, e.g. the nearest city
  • You have an IP address and you’d like to find the location details of that address, such as New York or Sydney

The series is centred around Amazon cloud based tools. Even if you’re not familiar with Amazon Cloud but looking for a solution to questions similar to the ones outlined above I encourage you to read on – you might just find something useful.

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Combinable enumerations in C# .NET

April 10, 2015 Leave a comment

You’ve probably encountered cases with combined enum values using the pipe character, i.e. the “bitwise or” operator ‘|’:

Size.Large | Size.ExtraLarge

Let’s see an example of how to create such an enum.

The enumeration is decorated with the Flags attribute like in the following example:

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Using Amazon RedShift with the AWS .NET API Part 8: data warehousing and the star schema 2

April 9, 2015 1 Comment

Introduction

In the previous post we discussed the basics of data warehousing and the different commonly used database schemas associated with it. We also set up a couple of tables: one raw data table which we filled with some raw data records, two dimension tables and a fact table.

In this post we’ll build upon the existing tables and present a couple of useful Postgresql statements in RedShift. Keep in mind that Postgresql in RedShift is very limited compared to the full version so you often need to be resourceful.

Fill in the dimension tables

Recall that we have 2 dimension tables: DimUrl and DimCustomer. Both are referenced from the fact table by their primary keys. We haven’t added any data into them yet. We’ll do that now.

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How to pass any number of parameters into a method in C# .NET

April 8, 2015 1 Comment

You must have come across built-in methods in .NET where you can send any number of arguments into a method. E.g. string.Format has an overload where you can pass in a format string and then an array with the “params” modifier.

There’s nothing stopping you from using the same keyword to write a similar method, here’s an example:

public void MethodWithParams(int toBeMultiplied, params int[] multipliers)
{
	foreach (int m in multipliers)
	{ 
		Console.WriteLine(string.Format("{0} x {1} = {2}", toBeMultiplied, m, toBeMultiplied * m));
	}
}

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Implementing an indexer for your object with C# .NET

April 7, 2015 1 Comment

Indexers are used extensively when accessing items in an array or List:

Friend f = friends[2];

It’s fairly easy to implement your own indexer. Imagine a table with guests sitting around. We could implement an indexer to easily access guest #n.

The Guest object is simple with only one property:

public class Guest
{
	public string Name { get; set; }
}

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Using Amazon RedShift with the AWS .NET API Part 7: data warehousing and the star schema

April 5, 2015 1 Comment

Introduction

In the previous post we dived into Postgresql statement execution on a RedShift cluster using C# and ODBC. We saw how to execute a single statement or many of them at once. We also tested a parameterised query which can protect us from SQL injections.

In this post we’ll deviate from .NET a little and concentrate on the basics of data warehousing and data mining in RedShift. In particular we’ll learn about a popular schema type often used in conjunction with data mining: the star schema.

Star and snowflake schemas

I went through the basic characteristics of star and snowflake schemas elsewhere on this blog, I’ll copy the relevant parts here.

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Python language basics 13: our first Python application

April 5, 2015 1 Comment

Introduction

In the previous post we saw how to get the user’s input in a command window. In this post we saw how to construct a while loop in Python. In this post we’ll marry the two concepts and build our first “real” application which requires user input. We’ll put together a simple number-guessing game where the computer “thinks” of a number between two integers and the user has to keep guessing until they find the correct one.

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Python language basics 12: reading user input

April 4, 2015 1 Comment

Introduction

In the previous post we looked at how to construct a while-loop and what its purpose is. In this post we’ll quickly learn how read a user’s input.

As a reminder I use the free edition of the PyCharm IDE so all the printouts will be from that environment.

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Creating temporary files on Windows using C# .NET

April 3, 2015 3 Comments

It’s trivial to create a temporary file using the Path class in .NET. Let’s first see how to find the path to the current user’s temp folder:

string tempFolderPath = Path.GetTempPath();

In my case it returns C:\Users\andras.nemes\AppData\Local\Temp\ which is the same as the value of the TEMP environment variable at the user level on my PC.

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