[FIXED] How to calculate and print pearson correlation coefficient as a metric in keras model?

Issue

I have a keras model that I am trying to do regression with. I want to print the correlation between y's predicted by the model and the actual y's after each epoch. The model.fit() function only prints train and validation loss by default. How would I go about implementing this custom metric?

model = keras.Sequential(...some layers...) 
...
model.fit(
         X,
         y, 
         metrics = [correlation_fn]
         ) 

So that during training after each epoch, it prints something like

50261/50261 [==============================] - 100s 2ms/step - loss: 20.6613 - val_loss: 13.3205 - pearson correlation: 0.56 

Solution

I figured out a way myself! The only problem I have with this solution is the way I have used to calculate the size of a minibatch, it looks pretty ugly and I don't know if there is a better way to do it.

class CorrelationMetric(keras.metrics.Metric): 
    def __init__(self, name="correlation", **kwargs): 
        super(CorrelationMetric, self).__init__(name=name, **kwargs)
        self.correlation = self.add_weight(name="correlation", initializer="zeros")
        self.n = self.add_weight(name="n", initializer="zeros")
        self.x = self.add_weight(name="x", initializer="zeros")
        self.x_squared = self.add_weight(name="x_squared", initializer="zeros")
        self.y = self.add_weight(name="y", initializer="zeros")
        self.y_squared = self.add_weight(name="y_squared", initializer="zeros")
        self.xy = self.add_weight(name="xy", initializer="zeros")
        
    def update_state(self, y_true, y_pred, sample_weight=None): 
        self.n.assign_add(tf.reduce_sum(tf.cast((y_pred == y_true), "float32")))
        self.n.assign_add(tf.reduce_sum(tf.cast((y_pred != y_true), "float32")))
        self.xy.assign_add(tf.reduce_sum(tf.multiply(y_pred, y_true)))
        self.x.assign_add(tf.reduce_sum(y_pred))
        self.y.assign_add(tf.reduce_sum(y_true))
        self.x_squared.assign_add(tf.reduce_sum(tf.math.square(y_pred)))
        self.y_squared.assign_add(tf.reduce_sum(tf.math.square(y_true)))
        
    def result(self): 
        return (self.n * self.xy - self.x * self.y)/tf.math.sqrt((self.n * self.x_squared - tf.math.square(self.x)) * (self.n * self.y_squared - tf.math.square(self.y)))
        
    def reset_state(self): 
        self.n.assign(0.0)
        self.x.assign(0.0)
        self.x_squared.assign(0.0)
        self.y.assign(0.0)
        self.y_squared.assign(0.0)
        self.xy.assign(0.0)
        self.correlation.assign(0.0)

#later, use this metric in a model 
model.compile(X, y, ..args.., metrics=[CorrelationMetric()]) 

Answered By - Varun Gupta