def federated_reduce(value, zero, op):
"""Reduces `value` from `tff.CLIENTS` to `tff.SERVER` using a reduction `op`.
This method reduces a set of member constituents of a `value` of federated
type `T@CLIENTS` for some `T`, using a given `zero` in the algebra (i.e., the
result of reducing an empty set) of some type `U`, and a reduction operator
`op` with type signature `(<U,T> -> U)` that incorporates a single `T`-typed
member constituent of `value` into the `U`-typed result of partial reduction.
In the special case of `T` equal to `U`, this corresponds to the classical
notion of reduction of a set using a commutative associative binary operator.
The generalized reduction (with `T` not equal to `U`) requires that repeated
application of `op` to reduce a set of `T` always yields the same `U`-typed
result, regardless of the order in which elements of `T` are processed in the
course of the reduction.
Args:
value: A value of a TFF federated type placed at the `tff.CLIENTS`.
zero: The result of reducing a value with no constituents.
op: An operator with type signature `(<U,T> -> U)`, where `T` is the type of
the constituents of `value` and `U` is the type of `zero` to be used in
performing the reduction.
Returns:
A representation on the `tff.SERVER` of the result of reducing the set of
all member constituents of `value` using the operator `op` into a single
item.
Raises:
TypeError: If the arguments are not of the types specified above.
"""
factory = intrinsic_factory.IntrinsicFactory(
context_stack_impl.context_stack)
return factory.federated_reduce(value, zero, op)
def federated_mean(value, weight=None):
"""Computes a `tff.SERVER` mean of `value` placed on `tff.CLIENTS`.
For values `v_1, ..., v_k`, and weights `w_1, ..., w_k`, this means
`sum_{i=1}^k (w_i * v_i) / sum_{i=1}^k w_i`.
Args:
value: The value of which the mean is to be computed. Must be of a TFF
federated type placed at `tff.CLIENTS`. The value may be structured, e.g.,
its member constituents can be named tuples. The tensor types that the
value is composed of must be floating-point or complex.
weight: An optional weight, a TFF federated integer or floating-point tensor
value, also placed at `tff.CLIENTS`.
Returns:
A representation at the `tff.SERVER` of the mean of the member constituents
of `value`, optionally weighted with `weight` if specified (otherwise, the
member constituents contributed by all clients are equally weighted).
Raises:
TypeError: If `value` is not a federated TFF value placed at `tff.CLIENTS`,
or if `weight` is not a federated integer or a floating-point tensor with
the matching placement.
"""
factory = intrinsic_factory.IntrinsicFactory(context_stack_impl.context_stack)
return factory.federated_mean(value, weight)
def federated_map(mapping_fn, value):
"""Maps a federated value pointwise using a mapping function.
The function `mapping_fn` is applied separately across the group of devices
represented by the placement type of `value`. For example, if `value` has
placement type `tff.CLIENTS`, then `mapping_fn` is applied to each client
individually. In particular, this operation does not alter the placement of
the federated value.
Args:
mapping_fn: A mapping function to apply pointwise to member constituents of
`value`. The parameter of this function must be of the same type as the
member constituents of `value`.
value: A value of a TFF federated type (or a value that can be implicitly
converted into a TFF federated type, e.g., by zipping) placed at
`tff.CLIENTS` or `tff.SERVER`.
Returns:
A federated value with the same placement as `value` that represents the
result of `mapping_fn` on the member constituent of `arg`.
Raises:
TypeError: If the arguments are not of the appropriate types.
"""
factory = intrinsic_factory.IntrinsicFactory(context_stack_impl.context_stack)
return factory.federated_map(mapping_fn, value)
def test_allows_assignable_but_not_equal_zero_and_reduction_types(self):
factory = intrinsic_factory.IntrinsicFactory(
context_stack_impl.context_stack)
element_type = tf.string
zero_type = computation_types.TensorType(tf.string, [1])
reduced_type = computation_types.TensorType(tf.string, [None])
@computations.tf_computation(reduced_type, element_type)
@computations.check_returns_type(reduced_type)
def append(accumulator, element):
return tf.concat([accumulator, [element]], 0)
@computations.tf_computation
@computations.check_returns_type(zero_type)
def zero():
return tf.convert_to_tensor(['The beginning'])
@computations.federated_computation(
computation_types.at_clients(element_type))
@computations.check_returns_type(
computation_types.at_server(reduced_type))
def collect(client_values):
return factory.federated_reduce(client_values, zero(), append)
self.assertEqual(collect.type_signature.compact_representation(),
'({string}@CLIENTS -> string[?]@SERVER)')
def federated_aggregate(value, zero, accumulate, merge, report):
"""Aggregates `value` from `tff.CLIENTS` to `tff.SERVER`.
This generalized aggregation function admits multi-layered architectures that
involve one or more intermediate stages to handle scalable aggregation across
a very large number of participants.
The multi-stage aggregation process is defined as follows:
* Clients are organized into groups. Within each group, a set of all the
member constituents of `value` contributed by clients in the group are first
reduced in a manner similar to `tff.federated_reduce` using reduction
operator `accumulate` with `zero` as the zero in the algebra. As described
in the documentation for `tff.federated_reduce`, if members of `value` are
of type `T`, and `zero` (the result of reducing an empty set) is of type
`U`, the reduction operator `accumulate` used at this stage should be of
type `(<U,T> -> U)`. The result of this stage is a set of items of type `U`,
one item for each group of clients.
* Next, the `U`-typed items generated by the preceding stage are merged using
the binary commutative associative operator `merge` of type `(<U,U> -> U)`.
This can be interpreted as a `tff.federated_reduce` using `merge` as the
reduction operator, and the same `zero` in the algebra. The result of this
stage is a single top-level `U` that emerges at the root of the hierarchy at
the `tff.SERVER`. Actual implementations may structure this step as a
cascade of multiple layers.
* Finally, the `U`-typed result of the reduction performed in the preceding
stage is projected into the result value using `report` as the mapping
function (for example, if the structures being merged consist of counters,
this final step might include computing their ratios).
Args:
value: A value of a TFF federated type placed at `tff.CLIENTS` to aggregate.
zero: The zero of type `U` in the algebra of reduction operators, as
described above.
accumulate: The reduction operator to use in the first stage of the process.
If `value` is of type `{T}@CLIENTS`, and `zero` is of type `U`, this
operator should be of type `(<U,T> -> U)`.
merge: The reduction operator to employ in the second stage of the process.
Must be of type `(<U,U> -> U)`, where `U` is as defined above.
report: The projection operator to use at the final stage of the process to
compute the final result of aggregation. If the intended result to be
returned by `tff.federated_aggregate` is of type `R@SERVER`, this operator
must be of type `(U -> R)`.
Returns:
A representation on the `tff.SERVER` of the result of aggregating `value`
using the multi-stage process described above.
Raises:
TypeError: If the arguments are not of the types specified above.
"""
factory = intrinsic_factory.IntrinsicFactory(
context_stack_impl.context_stack)
return factory.federated_aggregate(value, zero, accumulate, merge, report)
def federated_secure_sum(value, bitwidth):
"""Computes a sum at `tff.SERVER` of a `value` placed on the `tff.CLIENTS`.
This function computes a sum such that it should not be possible for the
server to learn any clients individual value. The specific algorithm and
mechanism used to compute the secure sum may vary depending on the target
runtime environment the computation is compiled for or executed on. See
https://research.google/pubs/pub47246/ for more information.
Not all executors support `tff.federated_secure_sum()`; consult the
documentation for the specific executor or executor stack you plan on using
for the specific of how it's handled by that executor.
The `bitwidth` argument represents the bitwidth of the aggregand, that is the
bitwidth of the input `value`. The federated secure sum bitwidth (i.e., the
bitwidth of the *sum* of the input `value`s over all clients) will be a
function of this bitwidth and the number of participating clients.
Example:
```python
value = tff.federated_value(1, tff.CLIENTS)
result = tff.federated_secure_sum(value, 2)
value = tff.federated_value([1, 1], tff.CLIENTS)
result = tff.federated_secure_sum(value, [2, 4])
value = tff.federated_value([1, [1, 1]], tff.CLIENTS)
result = tff.federated_secure_sum(value, [2, [4, 8]])
```
Note: To sum non-integer values or to sum integers with fewer constraints and
weaker privacy properties, consider using `federated_sum`.
Args:
value: An integer value of a TFF federated type placed at the `tff.CLIENTS`,
in the range [0, 2^bitwidth - 1].
bitwidth: An integer or nested structure of integers matching the structure
of `value`. If integer `bitwidth` is used with a nested `value`, the same
integer is used for each tensor in `value`.
Returns:
A representation of the sum of the member constituents of `value` placed
on the `tff.SERVER`.
Raises:
TypeError: If the argument is not a federated TFF value placed at
`tff.CLIENTS`.
"""
factory = intrinsic_factory.IntrinsicFactory(
context_stack_impl.context_stack)
return factory.federated_secure_sum(value, bitwidth)
def test_type_signature_with_non_federated_type(self):
factory = intrinsic_factory.IntrinsicFactory(
context_stack_impl.context_stack)
@computations.tf_computation(np.int32, np.int32)
def add(x, y):
return x + y
@computations.federated_computation(
computation_types.SequenceType(np.int32))
def foo(value):
return factory.sequence_reduce(value, 0, add)
self.assertEqual(foo.type_signature.compact_representation(),
'(int32* -> int32)')
def federated_collect(value):
"""Returns a federated value from `tff.CLIENTS` as a `tff.SERVER` sequence.
Args:
value: A value of a TFF federated type placed at the `tff.CLIENTS`.
Returns:
A stream of the same type as the member constituents of `value` placed at
the `tff.SERVER`.
Raises:
TypeError: If the argument is not a federated TFF value placed at
`tff.CLIENTS`.
"""
factory = intrinsic_factory.IntrinsicFactory(context_stack_impl.context_stack)
return factory.federated_collect(value)
def federated_eval(fn, placement):
"""Evaluates a federated computation at `placement`, returning the result.
Args:
fn: A no-arg TFF computation.
placement: The desired result placement (either `tff.SERVER` or
`tff.CLIENTS`).
Returns:
A federated value with the given placement `placement`.
Raises:
TypeError: If the arguments are not of the appropriate types.
"""
factory = intrinsic_factory.IntrinsicFactory(context_stack_impl.context_stack)
return factory.federated_eval(fn, placement)
def test_federated_map_all_equal(self):
factory = intrinsic_factory.IntrinsicFactory(
context_stack_impl.context_stack)
@computations.tf_computation(tf.int32)
def add_one(x):
return x + 1
@computations.federated_computation
def comp():
value = intrinsics.federated_value(10, placement_literals.CLIENTS)
return factory.federated_map_all_equal(add_one, value)
executor, _ = _create_test_executor()
result = _invoke(executor, comp)
for value in result:
self.assertEqual(value.numpy(), 10 + 1)
def federated_broadcast(value):
"""Broadcasts a federated value from the `tff.SERVER` to the `tff.CLIENTS`.
Args:
value: A value of a TFF federated type placed at the `tff.SERVER`, all
members of which are equal (the `tff.FederatedType.all_equal` property of
`value` is `True`).
Returns:
A representation of the result of broadcasting: a value of a TFF federated
type placed at the `tff.CLIENTS`, all members of which are equal.
Raises:
TypeError: If the argument is not a federated TFF value placed at the
`tff.SERVER`.
"""
factory = intrinsic_factory.IntrinsicFactory(context_stack_impl.context_stack)
return factory.federated_broadcast(value)
def federated_zip(value):
"""Converts an N-tuple of federated values into a federated N-tuple value.
Args:
value: A value of a TFF named tuple type, the elements of which are
federated values with the same placement.
Returns:
A federated value placed at the same location as the members of `value`, in
which every member component is a named tuple that consists of the
corresponding member components of the elements of `value`.
Raises:
TypeError: If the argument is not a named tuple of federated values with the
same placement.
"""
factory = intrinsic_factory.IntrinsicFactory(context_stack_impl.context_stack)
return factory.federated_zip(value)
def sequence_sum(value):
"""Computes a sum of elements in a sequence.
Args:
value: A value of a TFF type that is either a sequence, or a federated
sequence.
Returns:
The sum of elements in the sequence. If the argument `value` is of a
federated type, the result is also of a federated type, with the sum
computed locally and independently at each location (see also a discussion
on `sequence_map` and `sequence_reduce`).
Raises:
TypeError: If the arguments are of wrong or unsupported types.
"""
factory = intrinsic_factory.IntrinsicFactory(context_stack_impl.context_stack)
return factory.sequence_sum(value)
def test_type_signature_with_federated_type(self):
factory = intrinsic_factory.IntrinsicFactory(
context_stack_impl.context_stack)
@computations.tf_computation(np.int32, np.int32)
def add(x, y):
return x + y
@computations.federated_computation(
computation_types.FederatedType(
computation_types.SequenceType(np.int32),
placement_literals.CLIENTS))
def foo(value):
zero = intrinsics.federated_value(0, placement_literals.CLIENTS)
return factory.sequence_reduce(value, zero, add)
self.assertEqual(foo.type_signature.compact_representation(),
'({int32*}@CLIENTS -> {int32}@CLIENTS)')
def federated_sum(value):
"""Computes a sum at `tff.SERVER` of a `value` placed on the `tff.CLIENTS`.
To sum integer values with stronger privacy properties, consider using
`tff.federated_secure_sum`.
Args:
value: A value of a TFF federated type placed at the `tff.CLIENTS`.
Returns:
A representation of the sum of the member constituents of `value` placed
on the `tff.SERVER`.
Raises:
TypeError: If the argument is not a federated TFF value placed at
`tff.CLIENTS`.
"""
factory = intrinsic_factory.IntrinsicFactory(context_stack_impl.context_stack)
return factory.federated_sum(value)
def sequence_reduce(value, zero, op):
"""Reduces a TFF sequence `value` given a `zero` and reduction operator `op`.
This method reduces a set of elements of a TFF sequence `value`, using a given
`zero` in the algebra (i.e., the result of reducing an empty sequence) of some
type `U`, and a reduction operator `op` with type signature `(<U,T> -> U)`
that incorporates a single `T`-typed element of `value` into the `U`-typed
result of partial reduction. In the special case of `T` equal to `U`, this
corresponds to the classical notion of reduction of a set using a commutative
associative binary operator. The generalized reduction (with `T` not equal to
`U`) requires that repeated application of `op` to reduce a set of `T` always
yields the same `U`-typed result, regardless of the order in which elements
of `T` are processed in the course of the reduction.
One can also invoke `sequence_reduce` on a federated sequence, in which case
the reductions are performed pointwise; under the hood, we construct an
expression of the form
`federated_map(x -> sequence_reduce(x, zero, op), value)`. See also the
discussion on `sequence_map`.
Note: When applied to a federated value this function does the reduce
point-wise.
Args:
value: A value that is either a TFF sequence, or a federated sequence.
zero: The result of reducing a sequence with no elements.
op: An operator with type signature `(<U,T> -> U)`, where `T` is the type of
the elements of the sequence, and `U` is the type of `zero` to be used in
performing the reduction.
Returns:
The `U`-typed result of reducing elements in the sequence, or if the `value`
is federated, a federated `U` that represents the result of locally
reducing each member constituent of `value`.
Raises:
TypeError: If the arguments are not of the types specified above.
"""
factory = intrinsic_factory.IntrinsicFactory(
context_stack_impl.context_stack)
return factory.sequence_reduce(value, zero, op)
def sequence_map(mapping_fn, value):
"""Maps a TFF sequence `value` pointwise using a given function `mapping_fn`.
This function supports two modes of usage:
* When applied to a non-federated sequence, it maps individual elements of
the sequence pointwise. If the supplied `mapping_fn` is of type `T->U` and
the sequence `value` is of type `T*` (a sequence of `T`-typed elements),
the result is a sequence of type `U*` (a sequence of `U`-typed elements),
with each element of the input sequence individually mapped by `mapping_fn`.
In this mode of usage, `sequence_map` behaves like a compuatation with type
signature `<T->U,T*> -> U*`.
* When applied to a federated sequence, `sequence_map` behaves as if it were
individually applied to each member constituent. In this mode of usage, one
can think of `sequence_map` as a specialized variant of `federated_map` that
is designed to work with sequences and allows one to
specify a `mapping_fn` that operates at the level of individual elements.
Indeed, under the hood, when `sequence_map` is invoked on a federated type,
it injects `federated_map`, thus
emitting expressions like
`federated_map(a -> sequence_map(mapping_fn, x), value)`.
Args:
mapping_fn: A mapping function to apply pointwise to elements of `value`.
value: A value of a TFF type that is either a sequence, or a federated
sequence.
Returns:
A sequence with the result of applying `mapping_fn` pointwise to each
element of `value`, or if `value` was federated, a federated sequence
with the result of invoking `sequence_map` on member sequences locally
and independently at each location.
Raises:
TypeError: If the arguments are not of the appropriate types.
"""
factory = intrinsic_factory.IntrinsicFactory(
context_stack_impl.context_stack)
return factory.sequence_map(mapping_fn, value)
def federated_value(value, placement):
"""Returns a federated value at `placement`, with `value` as the constituent.
Deprecation warning: `tff.federated_value()` is deprecated, use
`tff.federated_eval()` instead.
Args:
value: A value of a non-federated TFF type to be placed.
placement: The desired result placement (either `tff.SERVER` or
`tff.CLIENTS`).
Returns:
A federated value with the given placement `placement`, and the member
constituent `value` equal at all locations.
Raises:
TypeError: If the arguments are not of the appropriate types.
"""
warnings.warn(
'Deprecation warning: tff.federated_value() is deprecated, use '
'tff.federated_eval() instead.', DeprecationWarning)
factory = intrinsic_factory.IntrinsicFactory(context_stack_impl.context_stack)
return factory.federated_value(value, placement)
