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Create a case operation.
tf.compat.v1.case(
pred_fn_pairs, default=None, exclusive=False, strict=False, name='case'
)
See also tf.switch_case
.
The pred_fn_pairs
parameter is a dict or list of pairs of size N.
Each pair contains a boolean scalar tensor and a python callable that
creates the tensors to be returned if the boolean evaluates to True.
default
is a callable generating a list of tensors. All the callables
in pred_fn_pairs
as well as default
(if provided) should return the same
number and types of tensors.
If exclusive==True
, all predicates are evaluated, and an exception is
thrown if more than one of the predicates evaluates to True
.
If exclusive==False
, execution stops at the first predicate which
evaluates to True, and the tensors generated by the corresponding function
are returned immediately. If none of the predicates evaluate to True, this
operation returns the tensors generated by default
.
tf.case
supports nested structures as implemented in
tf.contrib.framework.nest
. All of the callables must return the same
(possibly nested) value structure of lists, tuples, and/or named tuples.
Singleton lists and tuples form the only exceptions to this: when returned by
a callable, they are implicitly unpacked to single values. This
behavior is disabled by passing strict=True
.
If an unordered dictionary is used for pred_fn_pairs
, the order of the
conditional tests is not guaranteed. However, the order is guaranteed to be
deterministic, so that variables created in conditional branches are created
in fixed order across runs.
Example 1:
Pseudocode:
if (x < y) return 17;
else return 23;
Expressions:
f1 = lambda: tf.constant(17)
f2 = lambda: tf.constant(23)
r = tf.case([(tf.less(x, y), f1)], default=f2)
Example 2:
Pseudocode:
if (x < y && x > z) raise OpError("Only one predicate may evaluate to True");
if (x < y) return 17;
else if (x > z) return 23;
else return -1;
Expressions:
def f1(): return tf.constant(17)
def f2(): return tf.constant(23)
def f3(): return tf.constant(-1)
r = tf.case({tf.less(x, y): f1, tf.greater(x, z): f2},
default=f3, exclusive=True)
Args | |
---|---|
pred_fn_pairs
|
Dict or list of pairs of a boolean scalar tensor and a callable which returns a list of tensors. |
default
|
Optional callable that returns a list of tensors. |
exclusive
|
True iff at most one predicate is allowed to evaluate to True .
|
strict
|
A boolean that enables/disables 'strict' mode; see above. |
name
|
A name for this operation (optional). |
Returns | |
---|---|
The tensors returned by the first pair whose predicate evaluated to True, or
those returned by default if none does.
|
Raises | |
---|---|
TypeError
|
If pred_fn_pairs is not a list/dictionary.
|
TypeError
|
If pred_fn_pairs is a list but does not contain 2-tuples.
|
TypeError
|
If fns[i] is not callable for any i, or default is not
callable.
|
Eager Compatibility
Unordered dictionaries are not supported in eager mode when exclusive=False
.
Use a list of tuples instead.