Long and wide data – when to use what? : <p>I'm in the process of compiling data from different data sets into one data set for analysis. I'll be doing data exploration, trying different things to find out what regularities may be hidden in the data, so I don't currently have a specific method in mind. Now I'm wondering if I should compile my data into long or wide format.</p>

<p><strong>Which format should I use, and why?</strong></p>

<p>I understand that data can be reshaped from long to wide or vice versa, but the mere existence of this functionality implies that the need to reshape sometimes arises and this need in turn implies that a specific format might be better suited for a certain task. So when do I need which format, and why?</p>

<p>I'm not asking about performance. That has been covered in other questions.</p>
