@extends('template')

@section('title')
	Reference: how to make a pie chart
@stop

@section('content')
# How to make a pie chart (ice cream)
We will need to import pyplot to make pie charts:
```py
import matplotlib.pyplot as plt
import numpy as np
```

## Pie Charts
To create a [pyplot pie chart](http://matplotlib.org/api/pyplot_api.html#matplotlib.pyplot.pie), you'll need two lists:

+ (required) A list of numbers indicating the size of each pie slice.
+ (optional) A list of labels for those slices


```py
icecreamPreferences = [30,50,10,6] # fyi: does not have to sum to 100
iceCreamLabels = ['Strawberry', 'Chocolate', 'Vanilla','Banana']
```

Those two lists can then be passed to the `pie()` function:

```py
# Setting the figure size is important-
# without it, you'll get a squished pie chart (no one likes squished pie)
plt.figure('Pie Chart Example', figsize=(4,4), facecolor='white')

plt.pie(icecreamPreferences,labels=iceCreamLabels)

plt.show()
```

<img src="pie-chart-basic.png" style="max-width:324px">



## Colors
To customize the colors of your slices, add the `colors` parameter when invoking `pie()` and pass it a list of colors:

```py
sliceColors = ['pink', 'chocolate', 'ivory','yellow']
plt.pie(icecreamPreferences,labels=iceCreamLabels,colors=sliceColors)
```

<img src="pie-chart-with-colors.png" style="max-width:324px">

In our ice cream flavor examples, the colors we choose are important because they match the flavors.

In some pie charts though, the color won't matter, just as long as there is a variety. In these cases, you can create a list of colors using [pyplot's colormap](http://scipy.github.io/old-wiki/pages/Cookbook/Matplotlib/Show_colormaps) feature.

Example:

```py
colormap = plt.cm.Set2
numberOfSlices = len(icecreamPreferences)
sliceColors = colormap(np.linspace(0., 1., numberOfSlices))

# Example resulting sliceColors list:
# [[ 0.40000001  0.76078433  0.64705884  1.        ]
# [ 0.67058825  0.59869283  0.78562093  1.        ]
# [ 0.88366014  0.84967321  0.23267974  1.        ]
# [ 0.7019608   0.7019608   0.7019608   1.        ]]
```


## Start angle
By default, your pie chart starts at 0 degrees (red lines added to show degrees):

<img src="pie-chart-0-degrees.png" style="max-width:324px">

To customize this angle, utilize the `startangle` parameter when invoking `pie()`:

```py
plt.pie(
    icecreamPreferences,
    labels=iceCreamLabels,
    startangle=90
    )
```

<img src="pie-chart-90-degrees.png" style="max-width:324px">


## Displaying percentages on slices

Our pie chart is created using these slices:

```py
icecreamPreferences = [30,50,10,6]
```

The sum of these 4 values is 96.

So each slice size is determined by a fraction of that:

+ Slice 1: 30/96 = 31.25%
+ Slice 2: 50/96 = 52.08%
+ Slice 3: 10/96 = 10.42%
+ Slice 4: 6/96  = 6.25%

To label each slice with its percentage, add the `autopct` parameter when invoking `pie()`.

To customize how the percentage values are displayed, set `autopct` to a __format string__ such as as `%.2f` which will display the percentages as a floating point number (`f`) with 2 decimals (`.2`).

```py
plt.pie(
    icecreamPreferences,
    labels=iceCreamLabels,
    colors=sliceColors,
    startangle=90,
    autopct='%.2f'
    )
```

<img src="pie-chart-final-example.png" style="max-width:324px">



## Full example

```py
import matplotlib.pyplot as plt

# Set up data for the pie chart...
icecreamPreferences = [30,50,10,6] # does not have to sum to 100
iceCreamLabels      = ['Strawberry', 'Chocolate', 'Vanilla','Banana']

# Make the pie chart...
# facecolor is the background color of the canvas
# figsize controls the (x, y) dimensions of the plot
plt.figure('Pie Chart Example', figsize=(4,4), facecolor='white')

plt.title("Ice Cream Preferences")

sliceColors = ['pink', 'chocolate', 'ivory','yellow']
plt.pie(
    icecreamPreferences,
    labels=iceCreamLabels,
    colors=sliceColors,
    startangle=90,
    autopct='%.2f'
    )

plt.show()
```

## Fancy extras: changing text color of percents and labels
Let's say you wanted to change the color of the text of the percent labels and the text labels of each slice. You can do that.

It turns out the `plt.pie` returns a tuple of three pieces of information: `wedges, text, and sliceText`. If you save that tuple of information, then you can change the color as you like.


```py
wedges, text, sliceText = plt.pie(
    icecreamPreferencespbp,
    labels=iceCreamLabels,
    colors=sliceColors,
    startangle=90,
    autopct='%.2f'
    )
```
Let's take a closer look at that tuple:
+  `wedges`: the pie slices (we are not going to change anything with the wedges)
+  `text`: text labels outside the pie (eg. Vanilla, Chocolate, etc)
+ `sliceText`: text that labels the percent of each slice (eg. 10.42, 52.08, etc)


```py
for t in text:
   t.set_color('magenta')
```
<img src="magentapie.png" style="max-width:324px">

changes the color of the numerical labels (see below):

```py
for s in sliceText:
   s.set_color('deepskyblue')
```
<img src="bluepie.png" style="max-width:324px">

---

@include('/labs/lab09/_toc')

@stop