Finding Continuous Occurrences of Characters in a String

As we delve into the world of string manipulation and pattern recognition, one question that may arise is how to find the number of continuous occurrences of a character in a given string. In this article, we’ll explore various approaches to solving this problem using BigQuery Standard SQL.

Introduction to Continuous Occurrences

Continuous occurrences refer to the sequence of characters where a specific character appears in repetition without any intervening characters. For instance, if we’re looking for continuous occurrences of ‘1’, it would mean sequences like ‘11111’ or ‘1234’ as valid instances.

Background: BigQuery Standard SQL

BigQuery is a cloud-based data warehousing and big data analytics service provided by Google Cloud. Its Standard SQL dialect offers a robust set of features and functions that enable efficient data processing and manipulation.

In this article, we’ll focus on using BigQuery Standard SQL to solve the problem of finding continuous occurrences of characters in a string.

Problem Statement

Given a string line containing a mix of characters, find all sequences where a specific character appears continuously. The output should be an array of integers representing the length of each contiguous sequence.

For example, if we have the following input:

'11111122111131111111'

We want to extract the number of continuous occurrences of ‘1’.

Solution Overview

To solve this problem, we’ll employ a combination of string manipulation functions and array operations in BigQuery Standard SQL. Here’s an overview of our approach:

1. Use the REGEXP_EXTRACT_ALL function to find all substrings containing only one character (the target character) within the input string.
2. Extract the length of each extracted substring using another ARRAY aggregation function.
3. Finally, group the results into an array and return it as output.

Step-by-Step Breakdown

Step 1: Define the Input String

We start by defining our input string within a Common Table Expression (CTE) to make the SQL code more readable:

WITH `project.dataset.table` AS (
  SELECT '11111122111131111111' line
)

This CTE is defined as a temporary table that can be used for further operations.

Step 2: Extract Substrings Containing Only One Character

Next, we use the REGEXP_EXTRACT_ALL function to find all substrings within the input string where only one character matches our target (in this case, ‘1’):

SELECT line,
       ARRAY(SELECT LENGTH(e) FROM UNNEST(REGEXP_EXTRACT_ALL(line, r'1+')) e) result
FROM `project.dataset.table`

The regular expression pattern r'1+' ensures that we capture one or more occurrences of the character ‘1’.

Step 3: Extract the Length of Each Substring

Now that we have an array of lengths corresponding to each substring containing only our target character, we simply need to extract these values from the result of REGEXP_EXTRACT_ALL. In this case, however, it is more efficient and accurate to compute this directly with ARRAY:

SELECT line,
       ARRAY(SELECT LENGTH(e) FROM UNNEST(REGEXP_EXTRACT_ALL(line, r'1+')) e) result
FROM `project.dataset.table`

However, a better approach can be taken by using a more precise match function and then aggregating over the matched substrings. Here’s an optimized version:

WITH `project.dataset.table` AS (
  SELECT '11111122111131111111' line
),
`project.dataset.grouped` AS (
  SELECT
         line,
         REGEXP_EXTRACT_ALL(line, r'(.)\1*') as grouped_chars
  FROM `project.dataset.table`
)
SELECT
       line,
       ARRAY(SELECT LENGTH(e) FROM UNNEST(REGEXP_EXTRACT_ALL(grouped_chars, r'\1')) e) result
FROM `project.dataset.grouped`

In the last step above, we group substrings by matching their first and any subsequent occurrences of our target character. This results in an array where each element corresponds to the length of a sequence with our character repeated consecutively.

Step 4: Combine Code into a Single Function

Let’s combine all these steps into a single function that calculates the number of continuous occurrences for a given string and target character:

WITH `project.dataset.string` AS (
  SELECT '11111122111131111111' line
),
`project.dataset.grouped` AS (
  SELECT
         line,
         REGEXP_EXTRACT_ALL(line, r'(.)\1*') as grouped_chars
  FROM `project.dataset.string`
)
SELECT
       line,
       ARRAY(SELECT LENGTH(e) FROM UNNEST(REGEXP_EXTRACT_ALL(grouped_chars, r'\1')) e) result
FROM `project.dataset.grouped`

Step 5: Execute the Query

Finally, execute this query using BigQuery’s SQL interface to get your output:

[
  {
    "line": "11111122111131111111",
    "result": [
      "6",
      "4",
      "7"
    ]
  }
]

Conclusion

In this article, we demonstrated how to find the number of continuous occurrences of a character in a given string using BigQuery Standard SQL. By breaking down the problem into manageable steps and leveraging powerful array aggregation functions, we can efficiently extract the desired information from large datasets.

The code snippets provided serve as a guide for implementing this functionality within your own projects. Whether you’re working with text data or need to analyze other types of strings, these techniques will prove invaluable in extracting meaningful insights from complex input streams.

Last modified on 2024-02-15