[FIXED] pyplot.scatter() plots points but has no meaningful axes?

Issue

I am trying to make a simple scatterplot with Matplotlib. I am passing an Numpy array for x and another one for y:

df = df.to_numpy()    # this was originally a pandas DataFrame
print(df)

plt.scatter(df[:,1], df[:,2])
plt.show()

The print outputs:

[['B' '-693.3127738066283' '19.14412552031358']
 ['B' '-1633.974496310751' '40.13395450795514']
 ['B' '-2010.8973373308845' '-37.64969595561755']
 ...
 ['R' '-1034.7669874549774' '-76.93110447814361']
 ['R' '745.6579736997674' '-51.74835753276244']
 ['R' '-1473.8940519681794' '-28.58246870754514']]

However, the plot outputs this:

To give a better view of what's happening, if I plot only the first three datapoints it looks like this:

So the x- and y- coordinates are being "plotted", but the axes have no meaningful scale or value. Why is this happening, and how can I make a regular scatterplot?

Solution

As you can see from your prints, df contains only strings. matplotlib has no idea what to do with them.

Change:

plt.scatter(df[:,1], df[:,2])

With:

plt.scatter(df[:,1].astype(float), df[:,2].astype(float))

What it does is converting the arrays to numeric types with which matplotlib knows how to deal. Of course, this is assuming the arrays contain strings representing valid numbers only.

Answered By - user2246849