---
title: "analyzing-the-price-of-legos-with-python"
date: 2014-01-15
tags: post
---

# Analyzing the price of Legos with Python

Legos are perfect. I liked them as a kid, I liked them as a slightly older kid (even while pretending that I was too old for such things), and I like them now (having graduated from ninja temples to [recreations of Fallingwater](http://shop.lego.com/en-US/Fallingwater-21005)). There’s something about playing with them that brings out creativity and imagination: even though I might not tinker with them as much as I did many years ago, they evoke a very specific sort of joy that I can’t resist.

Which brings me to the downside of having such a childlike habit: as an adult, you have to buy your own toys.

And jeez, these little bricks can get expensive: that Fallingwater set runs for $99.99, which is low compared to some of the “grown-up” sets dedicated to adult Lego fans like myself, who have more disposable income than self-control.

But have they always been so expensive?

To answer this question, I needed to get as much data about Legos as I could find. Thankfully, I found [BrickSet](http://www.brickset.com/), a sort of Lego database, which comes with its own handy export feature so I didn’t even have to bother with scraping. (I uploaded [a .csv of their entire data](https://gist.github.com/jmduke/8130034) as a Gist to avoid hammering their servers, but I recommend checking out the site — pretty neat stuff.)

### Assumptions and Notes

Worth noting a few things here:

*   Obviously the integrity of my analysis is limited by the integrity of the data. While I couldn’t find a better source than BrickSet, I’m sure its still missing a few sets and details.
    
*   I’m filtering out any sets with less than two pieces or a price of less than two dollars. Notably, this excludes items listed as ‘sets’ that don’t have any actual pieces.
    
*   I’m not taking inflation into account.
    
*   These graphs are drawn with the wonderful [python-nvd3](https://github.com/areski/python-nvd3/) library.
    
*   Prices are in USD.
    

Alright, that’s all the boring stuff. Let’s get started!

```
import pandas as pd
import numpy as np
from nvd3 import lineChart, discreteBarChart

filename = 'legos.csv'
outfile = open('legos.html', 'w')

# Main charting function.  Pretty ugly.
def print_chart(name, df, bar=False):
    width = 800
    height = 300

    xdata = list(df.keys())
    try:
        xdata = map(lambda x: float(x), xdata)
    except:
        pass

    ydata = list(df.values)

    if bar:
        chart = discreteBarChart(name=name.replace(" ", ""), height=height, width=width)
        chart.add_serie(name=name, y=ydata, x=xdata)
    else:
        chart = lineChart(name=name.replace(" ", ""), height=height, width=width, x_axis_format='')
        extra_serie = {"date_format": "%Y"}
        chart.add_serie(name=name, y=ydata, x=xdata)
    chart.buildcontent()
    outfile.write(chart.htmlcontent)

# Some boring parsing
data = pd.read_csv(filename)
data.fillna(0)
data = data[(data['Pieces'] > 1) & (data['USPrice'] > 1)]
```

### Price over time

The first thing I wanted to check was the obvious hypothesis: your average Lego set has gotten more expensive over time.

Let’s take a look:

```
print_chart("Price over time", data.groupby('Year')['USPrice'].mean())
```

At first glance, it looks like, yes, [1](#fn:1) price is increasing steadily over time. However, raw price per set is something of a flawed metric: after all, a $200 set with one thousand pieces is a better deal than a $10 set with twenty. What happens if we look at price per brick, instead of just price?

```
data['$/p'] = data['USPrice'] / data['Pieces']
print_chart("Price per brick over time", data.groupby('Year')['$/p'].mean())
```

Well, that’s certainly a different picture. Price per brick appears to have peaked in the early nineties and slowly come back to earth since then, where it hovers around a quarter.

### Price per brand

So, price hasn’t particularly increased over time. Another popular hypothesis is that Lego’s profits has come from the premium they charge for licensed sets: from the perennial Star Wars [2](#fn:2) sets to more adventurous collaborations like [The Avengers](http://marvelsuperheroes.lego.com/en-us/default.aspx) and even [Minecraft](http://shop.lego.com/en-US/Minecraft-21102), its easy to imagine that the company imposes something of a ‘brand tax’ on these sets. Let’s group the sets by theme and see for ourselves:

```
print_chart("Average price per brick grouped by theme", data.groupby('Theme')['$/p'].mean().order(), bar=True)
```

Huh – not exactly what I was expecting. While it’s definitely true that the more generic Legos are cheaper – “Homemaker”, “Freestyle”, and “Classic” being amongst the cheapest themes – _The Lego Movie_ and _Minecraft_ [3](#fn:3) are also on the cheaper end of the spectrum. Instead, it looks like the real heavy hitters are the niche sets: those for children (“Education”, “Baby”) and for programmers and tinkerers (“Galidor”, “Mindstorms”).

### Should you buy in bulk?

```
print_chart("Price per brick grouped by pieces", data[(data['Pieces'] > 15)].groupby('Pieces')['$/p'].mean())
```

Short answer: yes.

Long answer: well, yeah, but after a certain point it won’t make too big of a difference. Those tiny accessory and minifig-heavy sets will kill your wallet in the long run, though.

### So, what’s changed?

For my money, the biggest thing that’s changed is my perception – and my tastes, I suppose, as the sets that catch my eye nowadays tend to be much more expensive than the simple (and ninja-filled) sets of my childhood.

Which is relevant in of itself: Lego’s push to appeal to the adults who grew up with the blocks is a relatively recent one, as they continue to segment their audience. This can be visualized (albeit roughly) by graphing standard deviation of prices over time, showing that the _range_ of prices itself has increased:

```
print_chart("Variance over time", data.groupby('Year')['USPrice'].agg({'variance' : np.std})['variance'])
```

* * *

1.  Remember, this is without taking inflation into account. [\[return\]](#fnref:1)
2.  I maintain that the dual-bladed lightsaber that I got with my Darth Maul lego is objectively the coolest thing ever. [\[return\]](#fnref:2)
3.  Though in Minecraft’s case, its because the thing is just a bunch of tiny 1x1 bricks. [\[return\]](#fnref:3)