ribs.archives.GridArchive¶

class ribs.archives.GridArchive(*, solution_dim, dims, ranges, learning_rate=1.0, threshold_min=-inf, epsilon=1e-06, qd_score_offset=0.0, seed=None, dtype=<class 'numpy.float64'>)[source]¶

An archive that divides each dimension into uniformly-sized cells.

This archive is the container described in Mouret 2015. It can be visualized as an n-dimensional grid in the measure space that is divided into a certain number of cells in each dimension. Each cell contains an elite, i.e. a solution that maximizes the objective function for the measures in that cell.

Note

The idea of archive thresholds was introduced in Fontaine 2022. Refer to our CMA-MAE tutorial for more info on thresholds, including the learning_rate and threshold_min parameters.

Parameters

solution_dim (int) – Dimension of the solution space.
dims (array-like of int) – Number of cells in each dimension of the measure space, e.g. [20, 30, 40] indicates there should be 3 dimensions with 20, 30, and 40 cells. (The number of dimensions is implicitly defined in the length of this argument).
ranges (array-like of (float, float)) – Upper and lower bound of each dimension of the measure space, e.g. [(-1, 1), (-2, 2)] indicates the first dimension should have bounds \([-1,1]\) (inclusive), and the second dimension should have bounds \([-2,2]\) (inclusive). ranges should be the same length as dims.
epsilon (float) – Due to floating point precision errors, we add a small epsilon when computing the archive indices in the index_of() method – refer to the implementation here. Pass this parameter to configure that epsilon.
learning_rate (float) – The learning rate for threshold updates.
threshold_min (float) – The initial threshold value for all the cells.
qd_score_offset (float) – Archives often contain negative objective values, and if the QD score were to be computed with these negative objectives, the algorithm would be penalized for adding new cells with negative objectives. Thus, a standard practice is to normalize all the objectives so that they are non-negative by introducing an offset. This QD score offset will be subtracted from all objectives in the archive, e.g., if your objectives go as low as -300, pass in -300 so that each objective will be transformed as objective - (-300).
seed (int) – Value to seed the random number generator. Set to None to avoid a fixed seed.
dtype (str or data-type) – Data type of the solutions, objectives, and measures. We only support "f" / np.float32 and "d" / np.float64.

Raises

ValueError – dims and ranges are not the same length.

Methods

`__iter__`()	Creates an iterator over the `Elite`'s in the archive.
`__len__`()	Number of elites in the archive.
`add`(solution_batch, objective_batch, ...[, ...])	Inserts a batch of solutions into the archive.
`add_single`(solution, objective, measures[, ...])	Inserts a single solution into the archive.
`as_pandas`([include_solutions, include_metadata])	Converts the archive into an `ArchiveDataFrame` (a child class of `pandas.DataFrame`).
`clear`()	Removes all elites from the archive.
`cqd_score`(iterations, target_points, ...[, ...])	Computes the CQD score of the archive.
`grid_to_int_index`(grid_index_batch)	Converts a batch of grid indices into a batch of integer indices.
`index_of`(measures_batch)	Returns archive indices for the given batch of measures.
`index_of_single`(measures)	Returns the index of the measures for one solution.
`int_to_grid_index`(int_index_batch)	Converts a batch of indices into indices in the archive's grid.
`retrieve`(measures_batch)	Retrieves the elites with measures in the same cells as the measures specified.
`retrieve_single`(measures)	Retrieves the elite with measures in the same cell as the measures specified.
`sample_elites`(n)	Randomly samples elites from the archive.

Attributes

`best_elite`	The elite with the highest objective in the archive.
`boundaries`	The boundaries of the cells in each dimension.
`cells`	Total number of cells in the archive.
`dims`	Number of cells in each dimension.
`dtype`	The dtype of the solutions, objective, and measures.
`empty`	Whether the archive is empty.
`epsilon`	Epsilon for computing archive indices.
`interval_size`	The size of each dim (upper_bounds - lower_bounds).
`learning_rate`	The learning rate for threshold updates.
`lower_bounds`	Lower bound of each dimension.
`measure_dim`	Dimensionality of the measure space.
`qd_score_offset`	The offset which is subtracted from objective values when computing the QD score.
`solution_dim`	Dimensionality of the solutions in the archive.
`stats`	Statistics about the archive.
`threshold_min`	The initial threshold value for all the cells.
`upper_bounds`	Upper bound of each dimension.

__iter__()¶

Creates an iterator over the Elite’s in the archive.

Example

for elite in archive:
    elite.sol
    elite.obj
    ...

__len__()¶: Number of elites in the archive.

add(solution_batch, objective_batch, measures_batch, metadata_batch=None)¶

Inserts a batch of solutions into the archive.

Each solution is only inserted if it has a higher objective than the threshold of the corresponding cell. For the default values of learning_rate and threshold_min, this threshold is simply the objective value of the elite previously in the cell. If multiple solutions in the batch end up in the same cell, we only insert the solution with the highest objective. If multiple solutions end up in the same cell and tie for the highest objective, we insert the solution that appears first in the batch.

For the default values of learning_rate and threshold_min, the threshold for each cell is updated by taking the maximum objective value among all the solutions that landed in the cell, resulting in the same behavior as in the vanilla MAP-Elites archive. However, for other settings, the threshold is updated with the batch update rule described in the appendix of Fontaine 2022.

Note

The indices of all arguments should “correspond” to each other, i.e. solution_batch[i], objective_batch[i], measures_batch[i], and metadata_batch[i] should be the solution parameters, objective, measures, and metadata for solution i.

Parameters

solution_batch (array-like) – (batch_size, solution_dim) array of solution parameters.
objective_batch (array-like) – (batch_size,) array with objective function evaluations of the solutions.
measures_batch (array-like) – (batch_size, measure_dim) array with measure space coordinates of all the solutions.
metadata_batch (array-like) –
(batch_size,) array of Python objects representing metadata for the solution. For instance, this could be a dict with several properties.

Warning

Due to how NumPy’s asarray() automatically converts array-like objects to arrays, passing array-like objects as metadata may lead to unexpected behavior. However, the metadata may be a dict or other object which contains arrays, i.e. metadata_batch could be an array of dicts which contain arrays.

Returns

2-element tuple of (status_batch, value_batch) which describes the results of the additions. These outputs are particularly useful for algorithms such as CMA-ME.

status_batch (numpy.ndarray of int): An array of integers which represent the “status” obtained when attempting to insert each solution in the batch. Each item has the following possible values:
- 0: The solution was not added to the archive.
- 1: The solution improved the objective value of a cell which was already in the archive.
- 2: The solution discovered a new cell in the archive.
All statuses (and values, below) are computed with respect to the current archive. For example, if two solutions both introduce the same new archive cell, then both will be marked with 2.

The alternative is to depend on the order of the solutions in the batch – for example, if we have two solutions a and b which introduce the same new cell in the archive, a could be inserted first with status 2, and b could be inserted second with status 1 because it improves upon a. However, our implementation does not do this.

To convert statuses to a more semantic format, cast all statuses to AddStatus e.g. with [AddStatus(s) for s in status_batch].
value_batch (dtype): An array with values for each solution in the batch. With the default values of learning_rate = 1.0 and threshold_min = -np.inf, the meaning of each value depends on the corresponding status and is identical to that in CMA-ME (Fontaine 2020):
- 0 (not added): The value is the “negative improvement,” i.e. the objective of the solution passed in minus the objective of the elite still in the archive (this value is negative because the solution did not have a high enough objective to be added to the archive).
- 1 (improve existing cell): The value is the “improvement,” i.e. the objective of the solution passed in minus the objective of the elite previously in the archive.
- 2 (new cell): The value is just the objective of the solution.
In contrast, for other values of learning_rate and threshold_min, each value is equivalent to the objective value of the solution minus the threshold of its corresponding cell in the archive.

Return type

tuple

Raises

ValueError – The array arguments do not match their specified shapes.
ValueError – objective_batch or measures_batch has non-finite values (inf or NaN).

add_single(solution, objective, measures, metadata=None)¶

Inserts a single solution into the archive.

The solution is only inserted if it has a higher objective than the threshold of the corresponding cell. For the default values of learning_rate and threshold_min, this threshold is simply the objective value of the elite previously in the cell. The threshold is also updated if the solution was inserted.

Note

To make it more amenable to modifications, this method’s implementation is designed to be readable at the cost of performance, e.g., none of its operations are modified. If you need performance, we recommend using add().

Parameters

solution (array-like) – Parameters of the solution.
objective (float) – Objective function evaluation of the solution.
measures (array-like) – Coordinates in measure space of the solution.
metadata (object) –
Python object representing metadata for the solution. For instance, this could be a dict with several properties.

Warning

Due to how NumPy’s asarray() automatically converts array-like objects to arrays, passing array-like objects as metadata may lead to unexpected behavior. However, the metadata may be a dict or other object which contains arrays.

Raises

ValueError – The array arguments do not match their specified shapes.
ValueError – objective is non-finite (inf or NaN) or measures has non-finite values.

Returns

2-element tuple of (status, value) describing the result of the add operation. Refer to add() for the meaning of the status and value.

Return type

tuple

as_pandas(include_solutions=True, include_metadata=False)¶

Converts the archive into an ArchiveDataFrame (a child class of pandas.DataFrame).

The implementation of this method in ArchiveBase creates a dataframe consisting of:

1 column of integers (np.int32) for the index, named index. See index_of() for more info.
measure_dim columns for the measures, named measure_0, measure_1, ...
1 column for the objectives, named objective
solution_dim columns for the solution parameters, named solution_0, solution_1, ...
1 column for the metadata objects, named metadata

In short, the dataframe looks like this:

index	measure_0	…	objective	solution_0	…	metadata
		…			…

Compared to pandas.DataFrame, the ArchiveDataFrame adds methods and attributes which make it easier to manipulate archive data. For more information, refer to the ArchiveDataFrame documentation.

Parameters

include_solutions (bool) – Whether to include solution columns.
include_metadata (bool) – Whether to include the metadata column. Note that methods like to_csv() may not properly save the dataframe since the metadata objects may not be representable in a CSV.

Returns

See above.

Return type

ArchiveDataFrame

clear()¶

Removes all elites from the archive.

After this method is called, the archive will be empty.

cqd_score(iterations, target_points, penalties, obj_min, obj_max, dist_max=None, dist_ord=None)¶

Computes the CQD score of the archive.

The Continuous Quality Diversity (CQD) score was introduced in Kent 2022.

Note

This method by default assumes that the archive has an upper_bounds and lower_bounds property which delineate the bounds of the measure space, as is the case in GridArchive, CVTArchive, and SlidingBoundariesArchive. If this is not the case, dist_max must be passed in, and target_points must be an array of custom points.

Parameters

iterations (int) – Number of times to compute the CQD score. We return the mean CQD score across these iterations.
target_points (int or array-like) – Number of target points to generate, or an (iterations, n, measure_dim) array which lists n target points to list on each iteration. When an int is passed, the points are sampled uniformly within the bounds of the measure space.
penalties (int or array-like) – Number of penalty values over which to compute the score (the values are distributed evenly over the range [0,1]). Alternatively, this may be a 1D array which explicitly lists the penalty values. Known as \(\theta\) in Kent 2022.
obj_min (float) – Minimum objective value, used when normalizing the objectives.
obj_max (float) – Maximum objective value, used when normalizing the objectives.
dist_max (float) – Maximum distance between points in measure space. Defaults to the distance between the extremes of the measure space bounds (the type of distance is computed with the order specified by dist_ord). Known as \(\delta_{max}\) in Kent 2022.
dist_ord – Order of the norm to use for calculating measure space distance; this is passed to numpy.linalg.norm() as the ord argument. See numpy.linalg.norm() for possible values. The default is to use Euclidean distance (L2 norm).

Returns

The mean CQD score obtained with iterations rounds of calculations.

Raises

RuntimeError – The archive does not have the bounds properties mentioned above, and dist_max is not specified or the target points are not provided.
ValueError – target_points or penalties is an array with the wrong shape.

grid_to_int_index(grid_index_batch)[source]¶

Converts a batch of grid indices into a batch of integer indices.

Refer to index_of() for more info.

Parameters: grid_index_batch (array-like) – (batch_size, measure_dim) array of indices in the archive grid.
Returns: (batch_size,) array of integer indices.
Return type: numpy.ndarray
Raises: ValueError – grid_index_batch is not of shape (batch_size, measure_dim)

index_of(measures_batch)[source]¶

Returns archive indices for the given batch of measures.

First, values are clipped to the bounds of the measure space. Then, the values are mapped to cells; e.g. cell 5 along dimension 0 and cell 3 along dimension 1.

At this point, we have “grid indices” – indices of each measure in each dimension. Since indices returned by this method must be single integers (as opposed to a tuple of grid indices), we convert these grid indices into integer indices with numpy.ravel_multi_index() and return the result.

It may be useful to have the original grid indices. Thus, we provide the grid_to_int_index() and int_to_grid_index() methods for converting between grid and integer indices.

As an example, the grid indices can be used to access boundaries of a measure value’s cell. For example, the following retrieves the lower and upper bounds of the cell along dimension 0:

# Access only element 0 since this method operates in batch.
idx = archive.int_to_grid_index(archive.index_of(...))[0]

lower = archive.boundaries[0][idx[0]]
upper = archive.boundaries[0][idx[0] + 1]

See boundaries for more info.

Parameters

measures_batch (array-like) – (batch_size, measure_dim) array of coordinates in measure space.

Returns

(batch_size,) array of integer indices representing the flattened grid coordinates.

Return type

numpy.ndarray

Raises

ValueError – measures_batch is not of shape (batch_size, measure_dim).
ValueError – measures_batch has non-finite values (inf or NaN).

index_of_single(measures)¶

Returns the index of the measures for one solution.

While index_of() takes in a batch of measures, this method takes in the measures for only one solution. If index_of() is implemented correctly, this method should work immediately (i.e. “out of the box”).

Parameters

measures (array-like) – (measure_dim,) array of measures for a single solution.

Returns

Integer index of the measures in the archive’s storage arrays.

Return type

int or numpy.integer

Raises

ValueError – measures is not of shape (measure_dim,).
ValueError – measures has non-finite values (inf or NaN).

int_to_grid_index(int_index_batch)[source]¶

Converts a batch of indices into indices in the archive’s grid.

Refer to index_of() for more info.

Parameters: int_index_batch (array-like) – (batch_size,) array of integer indices such as those output by index_of().
Returns: (batch_size, measure_dim) array of indices in the archive grid.
Return type: numpy.ndarray
Raises: ValueError – int_index_batch is not of shape (batch_size,).

retrieve(measures_batch)¶

Retrieves the elites with measures in the same cells as the measures specified.

This method operates in batch, i.e. it takes in a batch of measures and outputs an EliteBatch. Since EliteBatch is a namedtuple, it can be unpacked:

solution_batch, objective_batch, measures_batch, \
    index_batch, metadata_batch = archive.retrieve(...)

Or the fields may be accessed by name:

elite_batch = archive.retrieve(...)
elite_batch.solution_batch
elite_batch.objective_batch
elite_batch.measures_batch
elite_batch.index_batch
elite_batch.metadata_batch

If the cell associated with measures_batch[i] has an elite in it, then elite_batch.solution_batch[i], elite_batch.objective_batch[i], elite_batch.measures_batch[i], elite_batch.index_batch[i], and elite_batch.metadata_batch[i] will be set to the properties of the elite. Note that elite_batch.measures_batch[i] may not be equal to measures_batch[i] since the measures only need to be in the same archive cell.

If the cell associated with measures_batch[i] does not have any elite in it, then the corresponding outputs are set to empty values – namely:

elite_batch.solution_batch[i] will be an array of NaN
elite_batch.objective_batch[i] will be NaN
elite_batch.measures_batch[i] will be an array of NaN
elite_batch.index_batch[i] will be -1
elite_batch.metadata_batch[i] will be None

If you need to retrieve a single elite associated with some measures, consider using retrieve_single().

Parameters

measures_batch (array-like) – (batch_size, measure_dim) array of coordinates in measure space.

Returns

See above.

Return type

EliteBatch

Raises

ValueError – measures_batch is not of shape (batch_size, measure_dim).
ValueError – measures_batch has non-finite values (inf or NaN).

retrieve_single(measures)¶

Retrieves the elite with measures in the same cell as the measures specified.

While retrieve() takes in a batch of measures, this method takes in the measures for only one solution and returns a single Elite.

Parameters

measures (array-like) – (measure_dim,) array of measures.

Returns

If there is an elite with measures in the same cell as the measures specified, then this method returns an Elite where all the fields hold the info of that elite. Otherwise, this method returns an Elite filled with the same “empty” values described in retrieve().

Raises

ValueError – measures is not of shape (measure_dim,).
ValueError – measures has non-finite values (inf or NaN).

sample_elites(n)¶

Randomly samples elites from the archive.

Currently, this sampling is done uniformly at random. Furthermore, each sample is done independently, so elites may be repeated in the sample. Additional sampling methods may be supported in the future.

Since EliteBatch is a namedtuple, the result can be unpacked (here we show how to ignore some of the fields):

solution_batch, objective_batch, measures_batch, *_ = \
    archive.sample_elites(32)

Or the fields may be accessed by name:

elite = archive.sample_elites(16)
elite.solution_batch
elite.objective_batch
...

Parameters: n (int) – Number of elites to sample.
Returns: A batch of elites randomly selected from the archive.
Return type: EliteBatch
Raises: IndexError – The archive is empty.

property best_elite¶

The elite with the highest objective in the archive.

None if there are no elites in the archive.

Note

If the archive is non-elitist (this occurs when using the archive with a learning rate which is not 1.0, as in CMA-MAE), then this best elite may no longer exist in the archive because it was replaced with an elite with a lower objective value. This can happen because in non-elitist archives, new solutions only need to exceed the threshold of the cell they are being inserted into, not the objective of the elite currently in the cell. See #314 for more info.

Type: Elite

property boundaries¶

The boundaries of the cells in each dimension.

Entry i in this list is an array that contains the boundaries of the cells in dimension i. The array contains self.dims[i] + 1 entries laid out like this:

Archive cells:  | 0 | 1 |   ...   |    self.dims[i]    |
boundaries[i]:  0   1   2   self.dims[i] - 1     self.dims[i]

Thus, boundaries[i][j] and boundaries[i][j + 1] are the lower and upper bounds of cell j in dimension i. To access the lower bounds of all the cells in dimension i, use boundaries[i][:-1], and to access all the upper bounds, use boundaries[i][1:].

Type: list of numpy.ndarray

property cells¶

Total number of cells in the archive.

Type: int

property dims¶

Number of cells in each dimension.

Type: (measure_dim,) numpy.ndarray

property dtype¶

The dtype of the solutions, objective, and measures.

Type: data-type

property empty¶

Whether the archive is empty.

Type: bool

property epsilon¶

Epsilon for computing archive indices. Refer to the documentation for this class.

Type: dtype

property interval_size¶

The size of each dim (upper_bounds - lower_bounds).

Type: (measure_dim,) numpy.ndarray

property learning_rate¶

The learning rate for threshold updates.

Type: float

property lower_bounds¶

Lower bound of each dimension.

Type: (measure_dim,) numpy.ndarray

property measure_dim¶

Dimensionality of the measure space.

Type: int

property qd_score_offset¶

The offset which is subtracted from objective values when computing the QD score.

Type: float

property solution_dim¶

Dimensionality of the solutions in the archive.

Type: int

property stats¶

Statistics about the archive.

See ArchiveStats for more info.

Type: ArchiveStats

property threshold_min¶

The initial threshold value for all the cells.

Type: float

property upper_bounds¶

Upper bound of each dimension.

Type: (measure_dim,) numpy.ndarray