operations.py

#

This program is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

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This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

#

You should have received a copy of the GNU Lesser General Public License along with this program. If not, see http://www.gnu.org/licenses/.

from __future__ import unicode_literals

from collections import OrderedDict

from rows.plugins.utils import create_table
from rows.table import Table

#

Merge a list of Table objects using keys to group rows

def join(keys, tables):

#

Make new (merged) Table fields

    fields = OrderedDict()
    for table in tables:
        fields.update(table.fields)

#

TODO: may raise an error if a same field is different in some tables

#

Check if all keys are inside merged Table’s fields

    fields_keys = set(fields.keys())
    for key in keys:
        if key not in fields_keys:
            raise ValueError('Invalid key: "{}"'.format(key))

#

Group rows by key, without missing ordering

    none_fields = lambda: OrderedDict({field: None for field in fields.keys()})
    data = OrderedDict()
    for table in tables:
        for row in table:
            row_key = tuple([getattr(row, key) for key in keys])
            if row_key not in data:
                data[row_key] = none_fields()
            data[row_key].update(row._asdict())

    merged = Table(fields=fields)
    merged.extend(data.values())
    return merged

#

def transform(fields, function, *tables):
    "Return a new table based on other tables and a transformation function"

    new_table = Table(fields=fields)

    for table in tables:
        for row in filter(bool, map(lambda row: function(row, table), table)):
            new_table.append(row)

    return new_table

#

def transpose(table, fields_column, *args, **kwargs):
    field_names = []
    new_rows = [{} for _ in range(len(table.fields) - 1)]
    for row in table:
        row = row._asdict()
        field_name = row[fields_column]
        field_names.append(field_name)
        del row[fields_column]
        for index, value in enumerate(row.values()):
            new_rows[index][field_name] = value

    table_rows = [[row[field_name] for field_name in field_names] for row in new_rows]
    return create_table([field_names] + table_rows, *args, **kwargs)