68 lines
2.3 KiB
Python
68 lines
2.3 KiB
Python
#!/usr/bin/env python
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# pylint: disable=W0212
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from collections import OrderedDict
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from agate.exceptions import DataTypeError
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from agate.rows import Row
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@classmethod
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def merge(cls, tables, row_names=None, column_names=None):
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"""
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Create a new table from a sequence of similar tables.
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This method will not carry over row names from the merged tables, but new
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row names can be specified with the :code:`row_names` argument.
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It is possible to limit the columns included in the new :class:`.Table`
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with :code:`column_names` argument. For example, to only include columns
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from a specific table, set :code:`column_names` equal to
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:code:`table.column_names`.
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:param tables:
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An sequence of :class:`.Table` instances.
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:param row_names:
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See :class:`.Table` for the usage of this parameter.
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:param column_names:
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A sequence of column names to include in the new :class:`.Table`. If
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not specified, all distinct column names from `tables` are included.
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:returns:
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A new :class:`.Table`.
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"""
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from agate.table import Table
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new_columns = OrderedDict()
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for table in tables:
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for i in range(0, len(table.columns)):
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if column_names is None or table.column_names[i] in column_names:
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column_name = table.column_names[i]
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column_type = table.column_types[i]
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if column_name in new_columns:
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if not isinstance(column_type, type(new_columns[column_name])):
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raise DataTypeError('Tables contain columns with the same names, but different types.')
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else:
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new_columns[column_name] = column_type
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column_keys = tuple(new_columns.keys())
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column_types = tuple(new_columns.values())
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rows = []
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for table in tables:
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# Performance optimization for identical table structures
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if table.column_names == column_keys and table.column_types == column_types:
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rows.extend(table.rows)
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else:
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for row in table.rows:
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data = []
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for column_key in column_keys:
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data.append(row.get(column_key, None))
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rows.append(Row(data, column_keys))
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return Table(rows, column_keys, column_types, row_names=row_names, _is_fork=True)
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