Check if NaN in Tensorflow

Question

I would like to check a tensorflow variable and set it to zero if it is NaN.

How can I do this? The following trick seems not to work:

if tf.is_nan(v) is True:
    v = 0.0

Ventilation

Are you certain that is_nan() returns a boolean? – Peirsen

It returns a tensor of type boolean – Ventilation

What is the shape of v? is v a scalar? – Nigh

It is the cost of optimization. So, yes it is a tensor containing a scalar number. – Ventilation

Answer 1

If v is a 0d tensor, you might use tf.where to test and update the value:

import numpy as np

v = tf.constant(np.nan)                  # initialize a variable as nan  ​
v = tf.where(tf.is_nan(v), 0., v)
​
with tf.Session() as sess:    
    print(sess.run(v))

# 0.0

Nigh

Answer 2

For Tensorflow 2.0

you can you:

import tensorflow as tf

if tf.math.is_nan(v):
    print("v is NaN")

or with numpy

import numpy as np

if np.is_nan(v):
    print("v is NaN")

Famished

Very nice they've added this. This is so much cleaner than the original, but I guess it still is nice to know how to use tf.where and tf.is_nan if you need to do this kind of check on a vector (or batch) instead of on just a scalar. – Circuity

Answer 3

You could use tf.is_nan in combination with tf.cond to change values if the tensorflow value is NAN.

Prosthodontist

Answer 4

Libraries like numpy (in this case, tensorflow) often have their own boolean implementations, comparing the memory addresses of a custom boolean type, and CPython's built in using is is going to result in erratic behaviour.

Either just check implicit boolean-ness -> if tf.is_nan(v) or do a equality comparison if tf.is_nan(v) == True.

Peirsen

Answer 5

To make everything a tf operation, I used this to convert a single value to 0 if it's NaN:

value_not_nan = tf.dtypes.cast(tf.math.logical_not(tf.math.is_nan(value)), dtype=tf.float32)
tf.math.multiply_no_nan(value, value_not_nan)

Hindgut

Answer 6

I hope this can help you. math.is_nan

import math
if math.isnan(float(v)):
    v = 0.0

Scavenge

Not a tensorflow operaton, unfortunately useless answer – Groundsheet