What is the best way to visualize the relationship two categorical variables

Question

I am currently working on an ambulance dataset and one of my tasks is to find when a patient was misdiagnosed by the call dispatcher.

I have two codes; a dispatch code(what the dispatcher believes is wrong with the patient) and a hospital code(what a doctor decides the actual diagnosis is in hospital)

I'm looking for a way of visualizing the relationship between the two codes i.e. given ambulance code x what is the probability of each ambulance code being the outcome.

This can be computed using SQL pretty easily but I'm looking for a way to visualize/cluster it would be great. Any help would be appreciated.

EDIT: Some good feedback in the comments

firstly the dimensionality: Dispatch code can take 1 of 1722 unique values

hospital codes can take 1 of 1058 unique values

The two codes are entirely different an example would be as follows

Dispatcher 17D03:Unconscious 
Hospital R41:Other symptoms and signs involving cognitive functions and awareness

My interest is in visualizing the relationship. So for example given a dispatcher code of unconscious what are the most common hospital codes?

Again this is fairly easy to calculate numerically but a visualization would make it easier to explain to my stake holders.

Answer 1

You can use a confusion matrix to generate the heat map of your data.

Suppose you have:

labels = ['cardiac arrest', 'choking', 'seizure']
dispatch_code = ['cardiac arrest', 'choking', 'seizure', 'choking', 'seizure', 'seizure', 'cardiac arrest', 'cardiac arrest']
hospital_code = ['cardiac arrest', 'choking', 'cardiac arrest', 'choking', 'seizure', 'seizure', 'seizure', 'cardiac arrest']

Then you can plot with:

from sklearn.metrics import confusion_matrix
import matplotlib.pyplot as plt

cm = confusion_matrix(hospital_code, dispatch_code)
fig = plt.figure()
ax = fig.add_subplot(111)
cax = ax.matshow(cm)
plt.title('Confusion matrix of the classifier')
fig.colorbar(cax)
ax.set_xticklabels([''] + labels)
ax.set_yticklabels([''] + labels)
plt.xlabel('Predicted')
plt.ylabel('True')
plt.show()

This example shows that often there is a correct code coming from the dispatcher (yellow stripe in the middle). Cardiac arrest and seizure are often confused (blue) and chocking is never misclassified (purple).

Answer 2

If you are after counts of multi dimensional variables then Mosaicplot can help. In R there is a function from the graphics package called mosaicplot. It's one of base packages that come with R.

HairEyeColor , , Sex = Male

   Eye

Hair Brown Blue Hazel Green Black 32 11 10 3 Brown 53 50 25 15 Red 10 10 7 7 Blond 3 30 5 8

, , Sex = Female

   Eye

Hair Brown Blue Hazel Green Black 36 9 5 2 Brown 66 34 29 14 Red 16 7 7 7 Blond 4 64 5 8

mosiacplot(HairEyeColor)

Answer 3

In the end I ended up using an alluvial diagram on rawgraphs.