Streams and Vectorization | Apache Solr Reference Guide 7.5

This section of the user guide explores techniques for retrieving streams of data from Solr and vectorizing the numeric fields.

See the section Text Analysis and Term Vectors which describes how to vectorize text fields.

Streams

Streaming Expressions has a wide range of stream sources that can be used to retrieve data from Solr Cloud collections. Math expressions can be used to vectorize and analyze the results sets.

Below are some of the key stream sources:

random: Random sampling is widely used in statistics, probability and machine learning. The random function returns a random sample of search results that match a query. The random samples can be vectorized and operated on by math expressions and the results can be used to describe and make inferences about the entire population.
timeseries: The timeseries expression provides fast distributed time series aggregations, which can be vectorized and analyzed with math expressions.
knnSearch: K-nearest neighbor is a core machine learning algorithm. The knnSearch function is a specialized knn algorithm optimized to find the k-nearest neighbors of a document in a distributed index. Once the nearest neighbors are retrieved they can be vectorized and operated on by machine learning and text mining algorithms.
sql: SQL is the primary query language used by data scientists. The sql function supports data retrieval using a subset of SQL which includes both full text search and fast distributed aggregations. The result sets can then be vectorized and operated on by math expressions.
jdbc: The jdbc function allows data from any JDBC compliant data source to be combined with streams originating from Solr. Result sets from outside data sources can be vectorized and operated on by math expressions in the same manner as result sets originating from Solr.
topic: Messaging is an important foundational technology for large scale computing. The topic function provides publish/subscribe messaging capabilities by treating Solr Cloud as a distributed message queue. Topics are extremely powerful because they allow subscription by query. Topics can be use to support a broad set of use cases including bulk text mining operations and AI alerting.
nodes: Graph queries are frequently used by recommendation engines and are an important machine learning tool. The nodes function provides fast, distributed, breadth first graph traversal over documents in a Solr Cloud collection. The node sets collected by the nodes function can be operated on by statistical and machine learning expressions to gain more insight into the graph.
search: Ranked search results are a powerful tool for finding the most relevant documents from a large document corpus. The search expression returns the top N ranked search results that match any Solr query, including geo-spatial queries. The smaller set of relevant documents can then be explored with statistical, machine learning and text mining expressions to gather insights about the data set.

Assigning Streams to Variables

The output of any streaming expression can be set to a variable. Below is a very simple example using the random function to fetch three random samples from collection1. The random samples are returned as tuples which contain name/value pairs.

let(a=random(collection1, q="*:*", rows="3", fl="price_f"))

When this expression is sent to the /stream handler it responds with:

{
  "result-set": {
    "docs": [
      {
        "a": [
          {
            "price_f": 0.7927976
          },
          {
            "price_f": 0.060795486
          },
          {
            "price_f": 0.55128294
          }
        ]
      },
      {
        "EOF": true,
        "RESPONSE_TIME": 11
      }
    ]
  }
}

Creating a Vector with the col Function

The col function iterates over a list of tuples and copies the values from a specific column into an array.

The output of the col function is an numeric array that can be set to a variable and operated on by math expressions.

Below is an example of the col function:

let(a=random(collection1, q="*:*", rows="3", fl="price_f"),
    b=col(a, price_f))

{
  "result-set": {
    "docs": [
      {
        "b": [
          0.42105234,
          0.85237443,
          0.7566981
        ]
      },
      {
        "EOF": true,
        "RESPONSE_TIME": 9
      }
    ]
  }
}

Applying Math Expressions to the Vector

Once a vector has been created any math expression that operates on vectors can be applied. In the example below the mean function is applied to the vector assigned to variable b.

let(a=random(collection1, q="*:*", rows="15000", fl="price_f"),
    b=col(a, price_f),
    c=mean(b))

When this expression is sent to the /stream handler it responds with:

{
  "result-set": {
    "docs": [
      {
        "c": 0.5016035594638814
      },
      {
        "EOF": true,
        "RESPONSE_TIME": 306
      }
    ]
  }
}

Creating Matrices

Matrices can be created by vectorizing multiple numeric fields and adding them to a matrix. The matrices can then be operated on by any math expression that operates on matrices.

Note that this section deals with the creation of matrices from numeric data. The section Text Analysis and Term Vectors describes how to build TF-IDF term vector matrices from text fields.

Below is a simple example where four random samples are taken from different sub-populations in the data. The price_f field of each random sample is vectorized and the vectors are added as rows to a matrix. Then the sumRows function is applied to the matrix to return a vector containing the sum of each row.

let(a=random(collection1, q="market:A", rows="5000", fl="price_f"),
    b=random(collection1, q="market:B", rows="5000", fl="price_f"),
    c=random(collection1, q="market:C", rows="5000", fl="price_f"),
    d=random(collection1, q="market:D", rows="5000", fl="price_f"),
    e=col(a, price_f),
    f=col(b, price_f),
    g=col(c, price_f),
    h=col(d, price_f),
    i=matrix(e, f, g, h),
    j=sumRows(i))

When this expression is sent to the /stream handler it responds with:

{
  "result-set": {
    "docs": [
      {
        "j": [
          154390.1293375,
          167434.89453,
          159293.258493,
          149773.42769,
        ]
      },
      {
        "EOF": true,
        "RESPONSE_TIME": 9
      }
    ]
  }
}

Latitude / Longitude Vectors

The latlonVectors function wraps a list of tuples and parses a lat/lon location field into a matrix of lat/long vectors. Each row in the matrix is a vector that contains the lat/long pair for the corresponding tuple in the list. The row labels for the matrix are automatically set to the id field in the tuples. The lat/lon matrix can then be operated on by distance-based machine learning functions using the haversineMeters distance measure.

The latlonVectors function takes two parameters: a list of tuples and a named parameter called field, which tells the latlonVectors function which field to parse the lat/lon vectors from.

Below is an example of the latlonVectors.

let(a=random(collection1, q="*:*", fl="id, loc_p", rows="5"),
    b=latlonVectors(a, field="loc_p"))

When this expression is sent to the /stream handler it responds with:

{
  "result-set": {
    "docs": [
      {
        "b": [
          [
            42.87183530723629,
            76.74102353397778
          ],
          [
            42.91372904094898,
            76.72874889228416
          ],
          [
            42.911528804897564,
            76.70537292977619
          ],
          [
            42.91143870500213,
            76.74749913047408
          ],
          [
            42.904666267479705,
            76.73933236046092
          ]
        ]
      },
      {
        "EOF": true,
        "RESPONSE_TIME": 21
      }
    ]
  }
}

Matrices and Matrix Math Text Analysis and Term Vectors