jesse989 / plotly-lab-data-science-intro-000

Introduction

In this lab we will build out functions to help us plot visualizations in lessons going forward.

The Setup

Let's start by providing a function called plot which plots our data.

import plotly
from plotly.offline import iplot, init_notebook_mode

init_notebook_mode(connected=True)

def plot(figure):
    plotly.offline.iplot(figure)

To see our plot on the screen, we provide our plot function a dictionary. The dictionary has a key of data which points to a list of traces. Let's see it!

sample_trace = {'x': [1, 2, 3], 'y': [2, 3, 4]}
other_sample_trace = {'x': [2, 3, 4], 'y': [5, 3, 4]}
sample_figure = {'data': [sample_trace, other_sample_trace], 'layout': {'title': 'Our sample plot'}}
plot(sample_figure)

Ok, now that our plot function works, we need an easy way to create the following:

• traces
• figures
• layouts

Let's take these one by one. We'll start with a build_trace function that easily creates traces.

A function to create traces

build_trace

Write a build_trace function that can take in data that comes in the following format:

data = [{'x': 1, 'y': 1}, {'x': 3, 'y': 2}, {'x': 2, 'y': 5}]

And returns data like the commented out dictionary below:

data = [{'x': 1, 'y': 1}, {'x': 3, 'y': 2}, {'x': 2, 'y': 5}]
build_trace(data)
# {'x': [1, 3, 2], 'y': [1, 2, 5], 'mode': 'markers', 'name': 'data'}

So build_trace that takes in a list of data points as arguments and returns a dictionary with a key of x that points to a list of x values, and a key of y that points to a list of y values.

Note: Look at the parameters provided for build_trace. The arguments mode = 'markers' and name = 'data' may seem scary since we haven't seem them before. No need to worry! These are default arguments.

If no argument for mode or name is provided when we call the build_trace function, Python will automatically set these parameters to the value provided, which, in this case would be 'markers' for the mode and 'data' for the name.

def build_trace(data, mode = 'markers', name = 'data'):
    pass

So by default, if we just call build_trace(data) without specifying either a mode or a name, the function will automatically set these parameters to 'markers' and 'data' respectively.

data = [{'x': 1, 'y': 1}, {'x': 3, 'y': 2}, {'x': 2, 'y': 5}]
build_trace(data)
# {'x': [1, 3, 2], 'y': [1, 2, 5], 'mode': 'markers', 'name': 'data'}

If we want our build_trace function to take a different mode arguement, we add a second argument when we call the function which will overwrite the mode's default argument.

build_trace(data, 'scatter')
# {'x': [1, 3, 2], 'y': [1, 2, 5], 'mode': 'scatter', 'name': 'data'}

We could do the same thing with the name of the plot. This is useful for when we have more than one trace in the same plot.

Order matters. The value passed through as the name argument, should correspond to the value of the name key in our returned dictionary.

build_trace(data, 'markers', 'sample plot')
# {'x': [1, 3, 2], 'y': [1, 2, 5], 'mode': 'markers', 'name': 'sample plot'}

# trace0 = build_trace(data)

# trace0 = build_trace(data, 'markers')
# trace1 = build_trace(data, 'lines', 'my_trace')
# plot({'data':[trace0, trace1]})

trace_values

Now let's write another function to create a trace called trace_values. It works just like our build_trace function, except that it takes in a list of x_values and a list of y_values and returns our trace dictionary. We will use default argument again here in the same manner as before.

def trace_values(x_values, y_values, mode = 'markers', name="data"):
     pass

trace_values([1, 2, 3], [2, 4, 5])

# {'x': [1, 2, 3], 'y': [2, 4, 5], 'mode': 'markers', 'name': 'data'}

Now let's try to build a line trace with our newly defined trace_values function. We will set mode to 'lines' and the name of our trace to 'line trace'.

trace_values([1, 2, 3], [2, 4, 5], 'lines', 'line trace')
# {'x': [1, 2, 3], 'y': [2, 4, 5], 'mode': 'lines', 'name': 'line trace'}

From there, we can use our trace_values function to plot our chart.

Uncomment and run the code below

# trace2 = trace_values([1, 2, 3], [2, 4, 5], 'lines', 'line trace')
# plot({'data': [trace2]})

Creating layouts

Ok, now that we have built some functions to create traces, let's write a function to create a layout. Remember that our layout also can be passed to our plot function.

Uncomment and run the code below.

# plot({'data': [trace0, trace2], 'layout': {'title': 'Sample Title'}})

Our layout function should return a dictionary, just as it's defined in the above plot. We'll start by returning an empty dictionary then below we'll walk through building out the rest of the function.

def layout(x_range = None, y_range = None, options = {}):
    pass

layout()
# {}

Setting the xaxis and yaxis range

Oftentimes in building a layout, we want an easy way to set the range for the x and y axis. To set a range in the x-axis of $1$ through $4$ and a range of the y-axis of $2$ through $5$, we return a layout of the following structure.

{'xaxis': {'range': [1, 4]}, 'yaxis': {'range': [2, 5]}}

Let's start with adding functionality to the layout() function so it can set the range for the x-axis. (Hint: Google search Python's built-in isinstance() and update() functions.)

Add an argument of x_range returns a dictionary with a range set on the xaxis.

layout([1, 4])
# {'xaxis': {'range': [1, 4]}}

We want to ensure that when an x_range is not provided, an empty dictionary is still returned.

layout()
# {}

The x_range should be a default argument that sets x_range to None. Then, only add a key of xaxis to the dictionary layout when the x_range does not equal None.

layout() # {}

Now let's provide the same functionality for the y_range. When the y_range is provided we add a key of yaxis which points to a dictionary that expresses the y-axis range.

layout([1, 3], [4, 5])
# {'xaxis': {'range': [1, 3]}, 'yaxis': {'range': [4, 5]}}

Adding layout options

Now have the final argument of our layout function be options. The options argument should by default point to a dictionary. And whatever is provided as pointing to the options argument should be updated into the returned dictionary.

layout(options = {'title': 'foo'})

layout([1, 3], options = {'title': 'chart'})

# {'xaxis': {'range': [1, 3]}, 'title': 'chart'}

Ok, now let's see this layout function in action.

another_trace = trace_values([1, 2, 3], [6, 3, 1])
another_layout = layout([-1, 4], [0, 7], {'title': 'Going Down...'})
# plot({'data': [another_trace], 'layout': another_layout})

Finally, we'll modify the plot function for you so that it takes the data, and the layout as arguments.

def plot(traces = [], layout = {}):
    if not isinstance(traces, list): raise TypeError('first argument must be a list.  Instead is', traces)
    if not isinstance(layout, dict): raise TypeError('second argument must be a dict.  Instead is', layout)
    plotly.offline.iplot({'data': traces, 'layout': layout})

Uncomment the below code to see the updated plot function in action.

trace4 = trace_values([4, 5, 6], [10, 5, 1], mode = 'lines')
last_layout = layout(options = {'title': 'The big picture'})
plot([trace4], last_layout)

Summary

In this lab, we built out some methods so that we can easily create graphs going forward. We'll make good use of them in the lessons to come, as well as write new methods to help us easily display information in our charts.