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# Counterfactuals guided by prototypes on Boston housing dataset¶

This notebook goes through an example of prototypical counterfactuals using k-d trees to build the prototypes. Please check out this notebook for a more in-depth application of the method on MNIST using (auto-)encoders and trust scores.

In this example, we will train a simple neural net to predict whether house prices in the Boston area are above the median value or not. We can then find a counterfactual to see which variables need to be changed to increase or decrease a house price above or below the median value.

```
[1]:
```

```
import keras
from keras import backend as K
from keras.layers import Dense, Input
from keras.models import Model, load_model
from keras.utils import to_categorical
import matplotlib
%matplotlib inline
import matplotlib.pyplot as plt
import numpy as np
import os
from sklearn.datasets import load_boston
import tensorflow as tf
from alibi.explainers import CounterFactualProto
```

```
Using TensorFlow backend.
```

## Load and prepare Boston housing dataset¶

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[2]:
```

```
boston = load_boston()
data = boston['data']
target = boston['target']
feature_names = boston['feature_names']
```

Transform into classification task: target becomes whether house price is above the overall median or not

```
[3]:
```

```
y = np.zeros((target.shape[0],))
y[np.where(target > np.median(target))[0]] = 1
```

Remove categorical feature

```
[4]:
```

```
data = np.delete(data, 3, 1)
feature_names = np.delete(feature_names, 3)
```

Explanation of remaining features:

CRIM: per capita crime rate by town

ZN: proportion of residential land zoned for lots over 25,000 sq.ft.

INDUS: proportion of non-retail business acres per town

RM: average number of rooms per dwelling

AGE: proportion of owner-occupied units built prior to 1940

DIS: weighted distances to five Boston employment centres

RAD: index of accessibility to radial highways

TAX: full-value property-tax rate per USD10,000

PTRATIO: pupil-teacher ratio by town

B: 1000(Bk - 0.63)^2 where Bk is the proportion of blacks by town

LSTAT: % lower status of the population

Standardize data

```
[5]:
```

```
mu = data.mean(axis=0)
sigma = data.std(axis=0)
data = (data - mu) / sigma
```

Define train and test set

```
[6]:
```

```
idx = 475
x_train,y_train = data[:idx,:], y[:idx]
x_test, y_test = data[idx:,:], y[idx:]
y_train = to_categorical(y_train)
y_test = to_categorical(y_test)
```

## Train model¶

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```

```
np.random.seed(0)
tf.set_random_seed(0)
```

```
[8]:
```

```
def nn_model():
x_in = Input(shape=(12,))
x = Dense(40, activation='relu')(x_in)
x = Dense(40, activation='relu')(x)
x_out = Dense(2, activation='softmax')(x)
nn = Model(inputs=x_in, outputs=x_out)
nn.compile(loss='categorical_crossentropy', optimizer='sgd', metrics=['accuracy'])
return nn
```

```
[9]:
```

```
nn = nn_model()
nn.summary()
nn.fit(x_train, y_train, batch_size=128, epochs=500, verbose=0)
nn.save('nn_boston.h5')
```

```
_________________________________________________________________
Layer (type) Output Shape Param #
=================================================================
input_1 (InputLayer) (None, 12) 0
_________________________________________________________________
dense_1 (Dense) (None, 40) 520
_________________________________________________________________
dense_2 (Dense) (None, 40) 1640
_________________________________________________________________
dense_3 (Dense) (None, 2) 82
=================================================================
Total params: 2,242
Trainable params: 2,242
Non-trainable params: 0
_________________________________________________________________
```

```
[10]:
```

```
score = nn.evaluate(x_test, y_test, verbose=0)
print('Test accuracy: ', score[1])
```

```
Test accuracy: 0.8064516186714172
```

## Generate counterfactual guided by the nearest class prototype¶

Original instance:

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```

```
X = x_test[1].reshape((1,) + x_test[1].shape)
shape = X.shape
```

Run counterfactual:

```
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```

```
# set random seed
np.random.seed(1)
tf.set_random_seed(1)
# define model
nn = load_model('nn_boston.h5')
# get Keras session
sess = K.get_session()
# initialize explainer, fit and generate counterfactual
cf = CounterFactualProto(sess, nn, shape, use_kdtree=True, theta=10., max_iterations=1000,
feature_range=(x_train.min(axis=0), x_train.max(axis=0)),
c_init=1., c_steps=10)
cf.fit(x_train)
explanation = cf.explain(X)
sess.close()
K.clear_session()
```

```
No encoder specified. Using k-d trees to represent class prototypes.
```

The prediction flipped from 0 (value below the median) to 1 (above the median):

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```

```
print('Original prediction: {}'.format(explanation['orig_class']))
print('Counterfactual prediction: {}'.format(explanation['cf']['class']))
```

```
Original prediction: 0
Counterfactual prediction: 1
```

Let’s take a look at the counterfactual. To make the results more interpretable, we will first undo the pre-processing step and then check where the counterfactual differs from the original instance:

```
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```

```
orig = X * sigma + mu
counterfactual = explanation['cf']['X'] * sigma + mu
delta = counterfactual - orig
for i, f in enumerate(feature_names):
if np.abs(delta[0][i]) > 1e-4:
print('{}: {}'.format(f, delta[0][i]))
```

```
AGE: -21.56911332760376
LSTAT: -4.1864947634051575
```

So in order to increase the house price, the proportion of owner-occupied units built prior to 1940 should decrease by almost 22%. This is not surprising since the proportion for the observation is very high at 93.6%. Furthermore, the % of the population with “lower status” should decrease by 4%.

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[15]:
```

```
print('% owner-occupied units built prior to 1940: {}'.format(orig[0][5]))
print('% lower status of the population: {}'.format(orig[0][11]))
```

```
% owner-occupied units built prior to 1940: 93.6
% lower status of the population: 18.68
```

Clean up:

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```

```
os.remove('boston_nn.h5')
```