<p><div><div><div><div data-width="100" data-show-faces="false" data-send="true" data-layout="button_count" data-height="21" data-href="https://www.r-bloggers.com/because-its-friday-the-ikea-billy-index/"></div></div><div></div></div><div></div></div>
<div>
(This article was first published on <strong><a href="https://longhowlam.wordpress.com/2017/03/17/because-its-friday-the-ikea-billy-index/"> R – Longhow Lam's Blog</a></strong>, and kindly contributed to <a rel="nofollow" href="https://www.r-bloggers.com/">R-bloggers)</a> </div>
<p><img sizes="(max-width: 505px) 100vw, 505px" data-image-description="" data-orig-file="https://i1.wp.com/longhowlam.files.wordpress.com/2017/03/ikea.png?w=450&amp;ssl=1" data-orig-size="467,280" data-image-title="ikea" class="wp-image-2181" data-comments-opened="1" data-recalc-dims="1" data-attachment-id="2181" data-permalink="https://longhowlam.wordpress.com/2017/03/17/because-its-friday-the-ikea-billy-index/ikea/" alt="ikea" data-medium-file="https://i1.wp.com/longhowlam.files.wordpress.com/2017/03/ikea.png?w=450&amp;ssl=1?w=300" data-large-file="https://i1.wp.com/longhowlam.files.wordpress.com/2017/03/ikea.png?w=450&amp;ssl=1?w=440" data-image-meta="{&quot;aperture&quot;:&quot;0&quot;,&quot;credit&quot;:&quot;&quot;,&quot;camera&quot;:&quot;&quot;,&quot;caption&quot;:&quot;&quot;,&quot;created_timestamp&quot;:&quot;0&quot;,&quot;copyright&quot;:&quot;&quot;,&quot;focal_length&quot;:&quot;0&quot;,&quot;iso&quot;:&quot;0&quot;,&quot;shutter_speed&quot;:&quot;0&quot;,&quot;title&quot;:&quot;&quot;,&quot;orientation&quot;:&quot;0&quot;}" src="https://i1.wp.com/longhowlam.files.wordpress.com/2017/03/ikea.png?w=450&ssl=1"></p>
<h2>Introduction</h2>
<p>Because it is Friday, another ‘<strong><em>playful and frivolous</em></strong><em>‘</em> data exercise <img alt="🙂" class="wp-smiley" src="https://i0.wp.com/s0.wp.com/wp-content/mu-plugins/wpcom-smileys/twemoji/2/72x72/1f642.png?w=456&ssl=1" data-recalc-dims="1"></p>
<p>IKEA is more than a store, it is a very nice experience to go through. I can drop of my two kids at smàland, have some ‘quality time’ by walking around the store with my wife and eat some delicious <a target="_blank" rel="nofollow" href="http://www.food.com/recipe/ikea-swedish-meatballs-294387">Swedish meatballs</a>. Back at home, the IKEA furniture are a good <strong>‘relation-tester’:</strong> try building a big wardrobe together with your wife…..</p>
<p>The nice thing about IKEA is that you don’t have to come to the store for nothing, you can check the availability of an item on the IKEA website.</p>
<div><img src="https://i2.wp.com/media.licdn.com/mpr/mpr/AAEAAQAAAAAAAApTAAAAJGNiZjlmMmMxLWI5YjYtNDQzZC05ZTUxLWI4MmQ3YmJhZTVlMg.png?w=456&ssl=1" data-recalc-dims="1"></div>
<div></div>
<p>According to the website this gets refreshed every 1,5 hour. This brought me on an idea, if I check the availability every 1,5 hour I could get an idea of the number of items sold for a particular item.</p>
<h2>The IKEA Billy index</h2>
<p>Probably the <strong>most iconic item </strong>of IKEA is <strong>the Billy bookcase</strong>. Just in case you don’t know how this bookcase looks like, below is a picture, its simplicity in its most elegant way….</p>
<div><img src="https://i0.wp.com/media.licdn.com/mpr/mpr/AAEAAQAAAAAAAAuEAAAAJDI1ZjU2NjNhLWE4NGItNGMwZS1hOGJjLTExYmQyMGU1MzFhMw.png?w=456&ssl=1" data-recalc-dims="1"></div>
<div></div>
<p>For every 1,5 hour over the last few months I have checked the Dutch IKEA website for the availability of this famous item for the <strong>13 stores </strong>in the Netherlands, and calculated the <strong>negative difference</strong> between consecutive values.</p>
<p>The data that you get from this little <em>playful exercise</em> do not necessarily represent the numbers of Billy bookcases really sold. Maybe the stock got replenished in between, maybe items were moved internally to other stores. For example, if there are <strong>50</strong> Billy’s in Amsterdam available and 1,5 hour later there are <strong>45</strong> Billy’s, maybe 5 were sold, or 6 were sold and 1 got returned? replenished? I just don’t know!</p>
<p>All I see are movements in availability that might have been caused by products sold. But anyway, let’s call the movements of availability of the Billy’s <strong>the IKEA Billy index.</strong></p>
<h2>Some graphs of the Billy Index</h2>
<h3>Trends and forecasts</h3>
<p>Facebook released a nice R package, called <a target="_blank" rel="nofollow" href="http://github.com/facebookincubator/prophet"><strong>prophet</strong></a>. It can be used to perform forecasting on time series, and it is used internally by Facebook across many applications. I ran the prophet forecasting algorithm on the IKEA Billy index. The graph below shows the result.</p>
<div><img src="https://i1.wp.com/media.licdn.com/mpr/mpr/AAEAAQAAAAAAAAndAAAAJGI4YWE0Y2E3LTY3MjctNGVkMC1hOGNkLTVlNzdkMjZhYTczMA.png?w=450&ssl=1" data-recalc-dims="1"></div>
<div></div>
<p>There are some high peaks end of October, and end of December. We can also clearly see the Saturday peaks that the algorithm has picked up from the historic data and projected it in its future forecasts.</p>
<h3>Weekday and color</h3>
<p>The graph above showed already that on Saturdays the Billy index is high, what about the other days? The graph below shows the other days, it depicts the sum of the Ikea index per day since I started to collect this data (end of September). Wednesdays and Thursdays are less active days.</p>
<div><img src="https://i1.wp.com/media.licdn.com/mpr/mpr/AAEAAQAAAAAAAAr0AAAAJDYyODEzNzlkLTkzMmItNGYyYy05MGIzLWM1MDcxYTJiYjIzYg.png?resize=418%2C339&ssl=1" data-recalc-dims="1"></div>
<p> </p>
<p>Clearly most of the Billy’s are white.</p>
<h3>Correlations</h3>
<p>Does the daily Billy Index correlate with other data? I have used some Dutch <strong>weather data</strong> that can be downloaded from the Royal Netherlands Meteorological Institute (<a target="_blank" rel="nofollow" href="http://www.knmi.nl/over-het-knmi/about">KNMI</a>). The data consists of many daily weather variables. The graph below shows a correlation matrix of the IKEA Billy Index and only some of these weather variables.</p>
<div><img src="https://i1.wp.com/media.licdn.com/mpr/mpr/AAEAAQAAAAAAAAv3AAAAJGEyOGI5YWUwLTc3ODAtNDU4My05YTlkLWNmNmQwZThmNTlkMQ.png?w=450&ssl=1" data-recalc-dims="1"></div>
<p> </p>
<p>The only correlation with some meaning of the IKEA Billy Index and a weather variable is the <strong>Wind Speed</strong> (<strong>-0.19</strong>). Increasing wind speeds means decreasing Billy’s.</p>
<div><img src="https://i2.wp.com/media.licdn.com/mpr/mpr/AAEAAQAAAAAAAAttAAAAJDk3Y2IwMjVhLWM5NDQtNDBmMy04ZDU3LTM3ZjMyZmYyODAxYw.png?w=450&ssl=1" data-recalc-dims="1"></div>
<p> </p>
<p>It’s an explainable correlation of course…. <img alt="🙂" class="wp-smiley" src="https://i0.wp.com/s0.wp.com/wp-content/mu-plugins/wpcom-smileys/twemoji/2/72x72/1f642.png?w=456&ssl=1" data-recalc-dims="1"> You wouldn’t want to go to IKEA on (very) windy days, it is not easy to drive through strong winds with your Billy on top of your car.</p>
<div><img src="https://i1.wp.com/media.licdn.com/mpr/mpr/AAEAAQAAAAAAAAo_AAAAJDZhZTU2ZGUwLTE5ZjItNGIzNC04NzZlLThmZWQ4YTMyZWIyMw.png?resize=278%2C249&ssl=1" data-recalc-dims="1"></div>
<p> </p>
<p>Cheers, Longhow.</p>
<p> <a target="_blank" rel="nofollow" href="http://feeds.wordpress.com/1.0/gocomments/longhowlam.wordpress.com/2177/"><img alt="" src="http://feeds.wordpress.com/1.0/comments/longhowlam.wordpress.com/2177/" border="0"></a> <img alt="" src="https://i1.wp.com/pixel.wp.com/b.gif?resize=1%2C1&ssl=1" border="0" data-recalc-dims="1"></p>
<p>
<div>
<div>To <strong>leave a comment</strong> for the author, please follow the link and comment on their blog: <strong><a href="https://longhowlam.wordpress.com/2017/03/17/because-its-friday-the-ikea-billy-index/"> R – Longhow Lam's Blog</a></strong>.</div>
<hr>
<a rel="nofollow" href="https://www.r-bloggers.com/">R-bloggers.com</a> offers <strong><a rel="nofollow" href="https://feedburner.google.com/fb/a/mailverify?uri=RBloggers">daily e-mail updates</a></strong> about <a title="The R Project for Statistical Computing" rel="nofollow" href="https://www.r-project.org/">R</a> news and <a title="R tutorials" rel="nofollow" href="https://www.r-bloggers.com/search/tutorial">tutorials</a> on topics such as: <a title="Data science" rel="nofollow" href="https://www.r-bloggers.com/search/data%20science">Data science</a>, <a title="Big Data" rel="nofollow" href="https://www.r-bloggers.com/search/Big%20Data">Big Data, <a title="R jobs" rel="nofollow" href="https://www.r-users.com/">R jobs</a>, visualization (<a title="ggplot and ggplot2 tutorials" rel="nofollow" href="https://www.r-bloggers.com/search/ggplot2">ggplot2</a>, <a title="Boxplots using lattice and ggplot2 tutorials" rel="nofollow" href="https://www.r-bloggers.com/search/boxplot">Boxplots</a>, <a title="Maps and gis" rel="nofollow" href="https://www.r-bloggers.com/search/map">maps</a>, <a title="Animation in R" rel="nofollow" href="https://www.r-bloggers.com/search/animation">animation</a>), programming (<a title="RStudio IDE for R" rel="nofollow" href="https://www.r-bloggers.com/search/RStudio">RStudio</a>, <a title="Sweave and literate programming" rel="nofollow" href="https://www.r-bloggers.com/search/sweave">Sweave</a>, <a title="LaTeX in R" rel="nofollow" href="https://www.r-bloggers.com/search/LaTeX">LaTeX</a>, <a title="SQL and databases" rel="nofollow" href="https://www.r-bloggers.com/search/SQL">SQL</a>, <a title="Eclipse IDE for R" rel="nofollow" href="https://www.r-bloggers.com/search/eclipse">Eclipse</a>, <a title="git and github, Version Control System" rel="nofollow" href="https://www.r-bloggers.com/search/git">git</a>, <a title="Large data in R using Hadoop" rel="nofollow" href="https://www.r-bloggers.com/search/hadoop">hadoop</a>, <a title="Web Scraping of google, facebook, yahoo, twitter and more using R" rel="nofollow" href="https://www.r-bloggers.com/search/Web+Scraping">Web Scraping</a>) statistics (<a title="Regressions and ANOVA analysis tutorials" rel="nofollow" href="https://www.r-bloggers.com/search/regression">regression</a>, <a title="principal component analysis tutorial" rel="nofollow" href="https://www.r-bloggers.com/search/PCA">PCA</a>, <a title="Time series" rel="nofollow" href="https://www.r-bloggers.com/search/time+series">time series</a>, <a title="finance trading" rel="nofollow" href="https://www.r-bloggers.com/search/trading">trading</a>) and more...
<img height="1" alt="" width="1" src="http://feeds.feedburner.com/~r/RBloggers/~4/vqTe3K4RDXQ"></a></div>