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Posts by Eike Dehling

Machine Learning: Predicting house prices

February 16th, 2017 by
(http://blog.trifork.com/2017/02/16/machine-learning-predicting-house-prices/)

Recently i have followed an online course on machine learning to understand the current hype better. As with any subject though, only practice makes perfect, so i was looking to apply this new knowledge.

While looking to sell my house i found that would be a nice opportunity: Check if the prices a real estate agents estimates are in line with what the data suggests.

Linear regression algorithm should be a nice algorithm here, this algorithm will try to find the best linear prediction (y = a + bx1 + cx2 ; y = prediction, x1,x2 = variables). So for example this algorithm can estimate a price per square meter floor space or price per square meter of garden. For a more detailed explanation, check out the wikipedia page.

In the Netherlands funda is the main website for selling your house, so i have started by collecting some data, i used data on the 50 houses closest to my house. I’ve excluded apartments to try and limit data to properties similar to my house. For each house i collected the advertised price, usable floor space, lot size, number of (bed)rooms, type of house (row-house, corner-house, or detached) and year of construction (..-1930, 1931-1940, 1941-1950, 1950-1960, etc). These are the (easily available) variables i expected would influence house price the most. Type of house is a categorical variable, to use that in regression I modeled them as several binary (0/1) variables.

As preparation, i checked for relations between the variables using correlation. This showed me that much of the collected data does not seem to affect price: Only the floor space, lot size and number of rooms showed a significant correlation with house price.

For the regression analysis I only used the variables that had a significant correlation. Variables without correlation would not produce meaningful results anyway.

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Writing less code

November 23rd, 2016 by
(http://blog.trifork.com/2016/11/23/writing-less-code/)

Have you had that feeling that you have to write too much code to build simple functionality? Some things just feel repetitive, they feel you should be not have to write them yourself, instead a framework should make your life easier.

Recently I’ve been building a project in Java/Spring, and after some time I started wondering about alternatives and how to build the same functionality with less code.

There is lots of alternative frameworks and multiple ways of building rest endpoints in Java/Spring.

  • Building the controller/service/dao layers manually in Spring ; https://spring.io/guides/tutorials/bookmarks/
  • Using spring-data-rest to export your spring-data repositories ; https://spring.io/guides/gs/accessing-data-rest/
  • Groovy/grails RestfulController ; https://examples.javacodegeeks.com/jvm-languages/groovy/grails/grails-rest-example/
  • Python/django django-rest-framework ; http://www.django-rest-framework.org/tutorial/6-viewsets-and-routers/
  • etc

Examples

Below some abbreviated examples of how a simple rest endpoint looks for each approach. To actually run the examples, you’ll need check out the tutorials mentioned earlier. My goal here is a quick comparison of how you do things in each framework.

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