I am trying to find the cosine similarity between two columns of type array in a pyspark dataframe and add the cosine similarity as a third column, as shown below

The current implementation I have is:

import pyspark.sql.functions as func

def cosine_similarity(df, col1, col2):
    df_cosine = df.select(func.sum(df[col1] * df[col2]).alias('dot'), 
                          func.sqrt(func.sum(df[col1]**2)).alias('norm1'), 
                          func.sqrt(func.sum(df[col2] **2)).alias('norm2'))
    d = df_cosine.rdd.collect()[0].asDict()
    return d['dot']/(d['norm1'] * d['norm2'])

But I guess the above code only for works for columns with integer values. Is there anyway I would be able to extend the above function to achieve a similar behavior for array columns

CodePudding user response：

Yes above code is for number, not for array of numbers.

You can convert Array of numbers into pyspark Vectors https://spark.apache.org/docs/latest/api/python/reference/api/pyspark.ml.linalg.Vectors.html

And then call use dense and dot functions.

Example

from pyspark.ml.linalg import Vectors

x = Vectors.dense([1,2,3])
y = Vectors.dense([4,5,6])

x.dot(y)

Similarly, you can also use the norm function of Vector in pyspark for normalization.

CodePudding user response：

For the array of double, you can use the aggregate function.

df = spark.createDataFrame([[[0.1, 0.5, 2.0, 1.0], [3.0, 2.4, 0.2, 1.1]]], ['Col1', 'Col2'])
df.show()

 -------------------- -------------------- 
|                Col1|                Col2|
 -------------------- -------------------- 
|[0.1, 0.5, 2.0, 1.0]|[3.0, 2.4, 0.2, 1.1]|
 -------------------- -------------------- 

df.withColumn('dot',   f.expr('aggregate(arrays_zip(Col1, Col2), 0D, (acc, x) -> acc   (x.Col1 * x.Col2))')) \
  .withColumn('norm1', f.expr('sqrt(aggregate(Col1, 0D, (acc, x) -> acc   (x * x)))')) \
  .withColumn('norm2', f.expr('sqrt(aggregate(Col2, 0D, (acc, x) -> acc   (x * x)))')) \
  .withColumn('cosine', f.expr('dot / (norm1 * norm2)')) \
  .show(truncate=False)

 -------------------- -------------------- --- ----------------- ----------------- ------------------ 
|Col1                |Col2                |dot|norm1            |norm2            |cosine            |
 -------------------- -------------------- --- ----------------- ----------------- ------------------ 
|[0.1, 0.5, 2.0, 1.0]|[3.0, 2.4, 0.2, 1.1]|3.0|2.293468988235943|4.001249804748511|0.3269133956691457|
 -------------------- -------------------- --- ----------------- ----------------- ------------------