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Merge input cubes only once when computing lazy multimodel statistics #2518

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47 changes: 24 additions & 23 deletions esmvalcore/preprocessor/_multimodel.py
Original file line number Diff line number Diff line change
Expand Up @@ -480,7 +480,8 @@ def _compute_eager(
input_slices = cubes # scalar cubes
else:
input_slices = [cube[chunk] for cube in cubes]
result_slice = _compute(input_slices, operator=operator, **kwargs)
combined_cube = _combine(input_slices)
result_slice = _compute(combined_cube, operator=operator, **kwargs)
result_slices.append(result_slice)

try:
Expand All @@ -498,10 +499,13 @@ def _compute_eager(
return result_cube


def _compute(cubes: list, *, operator: iris.analysis.Aggregator, **kwargs):
def _compute(
cube: iris.cube.Cube,
*,
operator: iris.analysis.Aggregator,
**kwargs,
):
"""Compute statistic."""
cube = _combine(cubes)

with warnings.catch_warnings():
warnings.filterwarnings(
'ignore',
Expand All @@ -526,8 +530,6 @@ def _compute(cubes: list, *, operator: iris.analysis.Aggregator, **kwargs):

# Remove concatenation dimension added by _combine
result_cube.remove_coord(CONCAT_DIM)
for cube in cubes:
cube.remove_coord(CONCAT_DIM)

# some iris aggregators modify dtype, see e.g.
# https://numpy.org/doc/stable/reference/generated/numpy.ma.average.html
Expand All @@ -540,7 +542,7 @@ def _compute(cubes: list, *, operator: iris.analysis.Aggregator, **kwargs):
method=cell_method.method,
coords=cell_method.coord_names,
intervals=cell_method.intervals,
comments=f'input_cubes: {len(cubes)}')
)
result_cube.add_cell_method(updated_method)
return result_cube

Expand Down Expand Up @@ -596,27 +598,26 @@ def _multicube_statistics(
# Calculate statistics
statistics_cubes = {}
lazy_input = any(cube.has_lazy_data() for cube in cubes)
for stat in statistics:
(stat_id, result_cube) = _compute_statistic(cubes, lazy_input, stat)
combined_cube = None
for statistic in statistics:
stat_id = _get_stat_identifier(statistic)
logger.debug('Multicube statistics: computing: %s', stat_id)

(operator, kwargs) = _get_operator_and_kwargs(statistic)
(agg, agg_kwargs) = get_iris_aggregator(operator, **kwargs)
if lazy_input and agg.lazy_func is not None:
if combined_cube is None:
# Merge input cubes only once as this is can be computationally
# expensive.
combined_cube = _combine(cubes)
result_cube = _compute(combined_cube, operator=agg, **agg_kwargs)
else:
result_cube = _compute_eager(cubes, operator=agg, **agg_kwargs)
statistics_cubes[stat_id] = result_cube

return statistics_cubes


def _compute_statistic(cubes, lazy_input, statistic):
"""Compute a single statistic."""
stat_id = _get_stat_identifier(statistic)
logger.debug('Multicube statistics: computing: %s', stat_id)

(operator, kwargs) = _get_operator_and_kwargs(statistic)
(agg, agg_kwargs) = get_iris_aggregator(operator, **kwargs)
if lazy_input and agg.lazy_func is not None:
result_cube = _compute(cubes, operator=agg, **agg_kwargs)
else:
result_cube = _compute_eager(cubes, operator=agg, **agg_kwargs)
return (stat_id, result_cube)


def _multiproduct_statistics(
products,
statistics,
Expand Down