num_bridges for case where there are zero bridges about splink_graph HOT 3 CLOSED

Num bridges = 1 seems to only occur with cluster size = 2 in the synthetic data. Is there something wrong with the calculation?

from splink_graph.

This problem relates to the use of weight and distance in the graph calculation.

In particular, if you set the distance colname = 'weight' you get incorrect results:

from splink_graph.cluster_metrics import number_of_bridges
    
from pyspark.sql import Row
from pyspark.sql import functions as f 
data_list = [
    {"src": 1, "dst": 2, "weight":0.9, "cluster_id": 1},
    {"src": 2, "dst": 3, "weight":0.9, "cluster_id": 1},
    {"src": 3, "dst": 1, "weight":0.9, "cluster_id": 1},
        ]

data = spark.createDataFrame(Row(**x) for x in data_list)
cluster_num_bridges = number_of_bridges(data, distance_colname="weight")

cluster_num_bridges.toPandas()

Whilst my use of distance colname = 'weight' with the default weight_colname="weight" is illogical, we can avoid this problem altogether because the bridges calculation uses neither weight nor distance.

So we can simplify the function by removing both from the function signature

from splink_graph.

In the example code the problem is introduced here:
https://github.com/moj-analytical-services/splink_examples_synthetic_data/blob/4e649ac359a290a4749bf35b9ec58e7e20e2fe16/graph_analytics/person/uk_citizens_max_groupsize_20/basic/01_graph_analytics/job.py#L109

from splink_graph.