Learn to Code:

Zero to Sixty Data Analysis

Website: goo.gl/i5O6qR

Or wackywendell.github.io/learntocode

Goals

• Learn the basics of programming
• Learn to import, manipulate, and plot data

Why Python?

• Easy to learn and use
• Relatively simple
• Good for data analysis and plotting
• Good for machine learning, web development, scripting, text parsing, and many things.

Why Python?

Python is a full-featured language for generic programming, and data analysis, and it can also make beautiful plots. I made this plot last week. It took about 20-40 lines of code!

Installing Python

Install Anaconda, and get the Python 3.4 version!

http://continuum.io/downloads

Let's install it now.

• Windows or OS X: use the link above.
• Linux: Use the package manager, and/or ask for help.

If you already have Anaconda with Python 2:

1. Open a terminal

2. Run these lines:

    conda update --all                       # Update all the packages
    conda create -n py3 anaconda python=3    # Install a python 3 version
    source activate py3                      # Activate the python 3 version temporarily
    conda update --all                       # Update all the packages (for Python 3)
    ipython kernelspec install-self --user   # Allow the Python 2 version of ipython to 
                                             # have Python 3 notebooks

3. Any time you want to use Python 3, you'll need to run source activate py3

Let's try it!

1. Open the Terminal
2. Type ipython notebook
3. Press Enter
4. A window should open in your browser!
   • If it does not, look for text like
     The IPython Notebook is running at: http://localhost:8888/
   • Open that link
   • Try Ctrl-Click if necessary.
5. At the top right, click New, and under Notebooks click Python 3.

Let's do some plotting!

%pylab inline

Populating the interactive namespace from numpy and matplotlib

# This is hidden in the slides, but makes the plots small enough to fit in a slide
import matplotlib
phi = (1 + np.sqrt(5)) / 2.
matplotlib.rc('figure', figsize=(3,3/phi))

xs = np.linspace(0, np.pi*2)
ys = np.sin(xs)
plot(xs, ys)

[<matplotlib.lines.Line2D at 0x7f3f2a684cc0>]

Debugging

---

plot([1,2,3,4,5,6,7,8,9,10], [1,4,8,2,3,5,8,9,3,6,7])

---

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-18-ec77aff7bf8c> in <module>()
----> 1 plot([1,2,3,4,5,6,7,8,9,10], [1,4,8,2,3,5,8,9,3,6,7])

/usr/lib/python3.5/site-packages/matplotlib/pyplot.py in plot(*args, **kwargs)
   3097         ax.hold(hold)
   3098     try:
-> 3099         ret = ax.plot(*args, **kwargs)
   3100         draw_if_interactive()
   3101     finally:

[…]

/usr/lib/python3.5/site-packages/matplotlib/axes/_base.py in _xy_from_xy(self, x, y)
    221         y = np.atleast_1d(y)
    222         if x.shape[0] != y.shape[0]:
--> 223             raise ValueError("x and y must have same first dimension")
    224         if x.ndim > 2 or y.ndim > 2:
    225             raise ValueError("x and y can be no greater than 2-D")

ValueError: x and y must have same first dimension

plot([1,2,3,4,5,6,7,8,9,10], [1,4,8,2,3,5,8,9,3,6,7])

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-4-ec77aff7bf8c> in <module>()
----> 1 plot([1,2,3,4,5,6,7,8,9,10], [1,4,8,2,3,5,8,9,3,6,7])

/usr/lib/python3.5/site-packages/matplotlib/pyplot.py in plot(*args, **kwargs)
   3097         ax.hold(hold)
   3098     try:
-> 3099         ret = ax.plot(*args, **kwargs)
   3100         draw_if_interactive()
   3101     finally:

/usr/lib/python3.5/site-packages/matplotlib/axes/_axes.py in plot(self, *args, **kwargs)
   1371         lines = []
   1372 
-> 1373         for line in self._get_lines(*args, **kwargs):
   1374             self.add_line(line)
   1375             lines.append(line)

/usr/lib/python3.5/site-packages/matplotlib/axes/_base.py in _grab_next_args(self, *args, **kwargs)
    302                 return
    303             if len(remaining) <= 3:
--> 304                 for seg in self._plot_args(remaining, kwargs):
    305                     yield seg
    306                 return

/usr/lib/python3.5/site-packages/matplotlib/axes/_base.py in _plot_args(self, tup, kwargs)
    280             x = np.arange(y.shape[0], dtype=float)
    281 
--> 282         x, y = self._xy_from_xy(x, y)
    283 
    284         if self.command == 'plot':

/usr/lib/python3.5/site-packages/matplotlib/axes/_base.py in _xy_from_xy(self, x, y)
    221         y = np.atleast_1d(y)
    222         if x.shape[0] != y.shape[0]:
--> 223             raise ValueError("x and y must have same first dimension")
    224         if x.ndim > 2 or y.ndim > 2:
    225             raise ValueError("x and y can be no greater than 2-D")

ValueError: x and y must have same first dimension

Debugging

Writing code means fixing errors. Lots of errors.

• Don't be afraid to try new things and raise new errors.

• We'll get lots of practice with debugging in this series!

1. One step at a time
   • Write a little bit, check it, write the next bit
2. Isolate the problem
   • Cut out unnecessary code
   • Make a small example that fails the same way
3. Read the error messages
   • They usually say where the problem is, and what the problem is

Exiting IPython Notebook

1. Go back to the terminal
   • You'll see a line like [I 13:38:34.691 NotebookApp] Kernel started: 26190742-9d29-420f-9f0f-5c8aae026a62
2. Press Ctrl-C
   • It will ask you Shutdown this notebook server (y/[n])?
3. Press y then Enter
4. Close any windows in your browser

Getting back to the IPython Notebook

1. Open the Terminal
2. Type ipython notebook
3. Press Enter
4. A window should open in your browser!
   • If it does not, look for text like
     The IPython Notebook is running at: http://localhost:8888/
   • Open that link
   • Try Ctrl-Click if necessary.
5. Look for the notebook from before, probably named Untitled.ipynb, and click on it

Thanks for coming!

• Please fill out your feedback cards, and leave them by the door!
• Come on Thursday for our first Open Session!
• Try the practice problems, available on the website!