Filter

Filter

A filter takes a row as input and produces an alternate view of the row based on specified rules. For example, a row filter might trim down a row to include just the cells from columns matching a given regular expression, or might return all the cells of a row but not their values. More complicated filters can be composed out of these components to express requests such as, "within every column of a particular family, give just the two most recent cells which are older than timestamp X."

There are two broad categories of filters (true filters and transformers), as well as two ways to compose simple filters into more complex ones (Filter#interleave). They work as follows:

True filters alter the input row by excluding some of its cells wholesale from the output row. An example of a true filter is the Filter#value filter, which excludes cells whose values don't match the specified pattern. All regex true filters use RE2 syntax (https://github.com/google/re2/wiki/Syntax) and are evaluated as full matches. An important point to keep in mind is that RE2(.) is equivalent by default to RE2([^\n]), meaning that it does not match newlines. When attempting to match an arbitrary byte, you should therefore use the escape sequence '\C', which may need to be further escaped as '\C' in your client language.

Transformers alter the input row by changing the values of some of its cells in the output, without excluding them completely. Currently, the only supported transformer is the Filter#value strip filter, which replaces every cell's value with the empty string.

The total serialized size of a filter message must not exceed 4096 bytes, and filters may not be nested within each other to a depth of more than 20.

Use the following table for the various examples found throughout the filter documentation.

Row Key follows:gwashington follows:jadams follows:tjefferson
gwashington 1
tjefferson 1 1
jadams 1 1

Constructor

new Filter()

Methods

(static) convertToRegExpString(regex) → {string}

Parameters:
Name Type Description
regex regex | string | Array.<string>

Either a plain regex, a regex in string form or an array of strings.

Returns:
Type Description
string
Throws:

TypeError

Transforms Arrays into a simple regular expression for matching multiple values.

Example
const regexString = Filter.convertToRegExpString(['a', 'b', 'c']);
// => '(a|b|c)'

(static) createRange(start, end, key) → {object}

Creates a range object. All bounds default to inclusive.

Parameters:
Name Type Description
start object | string

Lower bound value.

end object | string

Upper bound value.

key string

Key used to create range value keys.

Returns:
Type Description
object
Example
const {Bigtable} = require('@google-cloud/bigtable');
const Filter = Bigtable.Filter;

const range = Filter.createRange('value1', 'value2', 'Test');
// {
//   startTestInclusive: new Buffer('value1'),
//   endTestExclusive: new Buffer('value2')
// }

//-
// It's also possible to pass in objects to specify inclusive/exclusive
// bounds.
//-
const upperBound = {
  value: 'value3',
  inclusive: false
};

const range = Filter.createRange(upperBound, null, 'Test2');
// => {
//   startTest2Exclusive: 'value3'
// }

(static) parse(filters) → {object}

Parameters:
Name Type Description
filters Array.<object>

The list of filters to be parsed.

Returns:
Type Description
object
Throws:

FilterError

Turns filters into proto friendly format.

Example
const filter = Filter.parse([
  {
    family: 'my-family',
  }, {
    column: 'my-column'
  }
]);
// {
//   chain: {
//     filters: [
//       {
//         familyNameRegexFilter: 'my-family'
//       },
//       {
//         columnQualifierRegexFilter: 'my-column'
//       }
//     ]
//   }
// }

all(pass)

Sets passAllFilter or blockAllFilter

Parameters:
Name Type Description
pass boolean

Whether to passAllFilter or blockAllFilter

Assign true for enabling passAllFilter and false for enabling blockAllFilter

Example
//-
// Matches all cells, regardless of input. Functionally equivalent to
// leaving `filter` unset, but included for completeness.
//-
const filter = {
  all: true
};

//-
// Does not match any cells, regardless of input. Useful for temporarily
// disabling just part of a filter.
//-
const filter = {
  all: false
};

column(column)

Matches only cells from columns whose qualifiers satisfy the given RE2 regex.

Parameters:
Name Type Description
column regex | string | object

Matching Column to filter with

Note that, since column qualifiers can contain arbitrary bytes, the '\C' escape sequence must be used if a true wildcard is desired. The '.' character will not match the new line character '\n', which may be present in a binary qualifier.

Example
//-
// Using the following filter, we would retrieve the `tjefferson` and
// `gwashington` columns.
//-
const filter = [
  {
    column: /[a-z]+on$/
  }
];

//-
// You can also provide a string (optionally containing regexp characters)
// for simple column filters.
//-
const filter = [
  {
    column: 'gwashington'
  }
];

//-
// Or you can provide an array of strings if you wish to match against
// multiple columns.
//-
const filter = [
  {
    column: [
      'gwashington',
      'tjefferson'
    ]
  }
];

//-
// If you wish to use additional column filters, consider using the following
// syntax.
//-
const filter = [
  {
    column: {
      name: 'gwashington'
    }
  }
];


//-
// <h4>Column Cell Limits</h4>
//
// Matches only the most recent number of versions within each column. For
// example, if the `versions` is set to 2, this filter would only match
// columns updated at the two most recent timestamps.
//
// If duplicate cells are present, as is possible when using an
// Filter#interleave filter, each copy of the cell is
// counted separately.
//-
const filter = [
  {
    column: {
      cellLimit: 2
    }
  }
];

//-
// <h4>Column Ranges</h4>
//
// Specifies a contiguous range of columns within a single column family.
// The range spans from <column_family>:<start_qualifier> to
// <column_family>:<end_qualifier>, where both bounds can be either
// inclusive or exclusive. By default both are inclusive.
//
// When the `start` bound is omitted it is interpreted as an empty string.
// When the `end` bound is omitted it is interpreted as Infinity.
//-
const filter = [
  {
    column: {
      family: 'follows',
      start: 'gwashington',
      end: 'tjefferson'
    }
  }
];

//-
// By default, both the `start` and `end` bounds are inclusive. You can
// override these by providing an object explicity stating whether or not it
// is `inclusive`.
//-
const filter = [
  {
    column: {
      family: 'follows',
      start: {
        value: 'gwashington',
        inclusive: false
      },
      end: {
        value: 'jadams',
        inclusive: false
      }
    }
  }
];

condition(condition)

A filter which evaluates one of two possible filters, depending on whether or not a test filter outputs any cells from the input row.

IMPORTANT NOTE: The test filter does not execute atomically with the pass and fail filters, which may lead to inconsistent or unexpected results. Additionally, condition filters have poor performance, especially when filters are set for the fail condition.

Parameters:
Name Type Description
condition object

Condition to filter.

Example
//-
// In the following example we're creating a filter that will check if
// `gwashington` follows `tjefferson`. If he does, we'll get all of the
// `gwashington` data. If he does not, we'll instead return all of the
// `tjefferson` data.
//-
const filter = [
  {
    condition: {
      // If `test` outputs any cells, then `pass` will be evaluated on the
      // input row. Otherwise `fail` will be evaluated.
      test: [
        {
          row: 'gwashington'
        },
        {
          family: 'follows'
        },
        {
          column: 'tjefferson'
        }
      ],

      // If omitted, no results will be returned in the true case.
      pass: [
        {
          row: 'gwashington'
        }
      ],

      // If omitted, no results will be returned in the false case.
      fail: [
        {
          row: 'tjefferson'
        }
      ]
    }
  }
];

family(family)

Matches only cells from columns whose families satisfy the given RE2 regex. For technical reasons, the regex must not contain the ':' character, even if it is not being used as a literal. Note that, since column families cannot contain the new line character '\n', it is sufficient to use '.' as a full wildcard when matching column family names.

Parameters:
Name Type Description
family regex

Expression to filter family

Example
const filter = [
  {
    family: 'follows'
  }
];

interleave(filters)

Applies several filters to the data in parallel and combines the results.

Parameters:
Name Type Description
filters object

The elements of "filters" all process a copy of the input row, and the results are pooled, sorted, and combined into a single output row. If multiple cells are produced with the same column and timestamp, they will all appear in the output row in an unspecified mutual order. All interleaved filters are executed atomically.

Example
//-
// In the following example, we're creating a filter that will retrieve
// results for entries that were either created between December 17th, 2015
// and March 22nd, 2016 or entries that have data for `follows:tjefferson`.
//-
const filter = [
  {
    interleave: [
      [
        {
          time: {
            start: new Date('December 17, 2015'),
            end: new Date('March 22, 2016')
          }
        }
      ],
      [
        {
          family: 'follows'
        },
        {
          column: 'tjefferson'
        }
      ]
    ]
  }
];

label(label)

Applies the given label to all cells in the output row. This allows the client to determine which results were produced from which part of the filter.

Parameters:
Name Type Description
label string

Label to determine filter point Values must be at most 15 characters in length, and match the RE2 pattern [a-z0-9\-]+

Due to a technical limitation, it is not currently possible to apply multiple labels to a cell. As a result, a chain filter may have no more than one sub-filter which contains a apply label transformer. It is okay for an Filter#interleave to contain multiple apply label transformers, as they will be applied to separate copies of the input. This may be relaxed in the future.

Example
const filter = {
  label: 'my-label'
};

row(row)

Matches only cells from rows whose keys satisfy the given RE2 regex. In other words, passes through the entire row when the key matches, and otherwise produces an empty row.

Parameters:
Name Type Description
row regex | string | Array.<string>

Row format to Filter

Note that, since row keys can contain arbitrary bytes, the '\C' escape sequence must be used if a true wildcard is desired. The '.' character will not match the new line character '\n', which may be present in a binary key.

Example
//-
// In the following example we'll use a regular expression to match all
// row keys ending with the letters "on", which would then yield
// `gwashington` and `tjefferson`.
//-
const filter = [
  {
    row: /[a-z]+on$/
  }
];

//-
// You can also provide a string (optionally containing regexp characters)
// for simple key filters.
//-
const filter = [
  {
    row: 'gwashington'
  }
];

//-
// Or you can provide an array of strings if you wish to match against
// multiple keys.
//-
const filter = [
  {
    row: [
      'gwashington',
      'tjefferson'
    ]
  }
];

//-
// If you wish to use additional row filters, consider using the following
// syntax.
//-
const filter = [
  {
    row: {
      key: 'gwashington'
    }
  }
];

//-
// <h4>Row Samples</h4>
//
// Matches all cells from a row with probability p, and matches no cells
// from the row with probability 1-p.
//-
const filter = [
  {
    row: {
      sample: 1
    }
  }
];

//-
// <h4>Row Cell Offsets</h4>
//
// Skips the first N cells of each row, matching all subsequent cells.
// If duplicate cells are present, as is possible when using an
// Filter#interleave, each copy of the cell is counted
// separately.
//-
const filter = [
  {
    row: {
      cellOffset: 2
    }
  }
];

//-
// <h4>Row Cell Limits</h4>
//
// Matches only the first N cells of each row.
// If duplicate cells are present, as is possible when using an
// Filter#interleave, each copy of the cell is counted
// separately.
//-
const filter = [
  {
    row: {
      cellLimit: 4
    }
  }
];

set(key, value)

Stores a filter object.

Parameters:
Name Type Description
key string

Filter name.

value *

Filter value.

sink(sink)

This filter is meant for advanced use only. Hook for introspection into the filter. Outputs all cells directly to the output of the read rather than to any parent filter. Despite being excluded by the qualifier filter, a copy of every cell that reaches the sink is present in the final result. As with an Filter#interleave filter, duplicate cells are possible, and appear in an unspecified mutual order.

Cannot be used within Filter#condition filter.

Parameters:
Name Type Description
sink boolean
Example
//-
// Using the following filter, a copy of every cell that reaches the sink is
// present in the final result, despite being excluded by the qualifier
// filter
//-
const filter = [
  {
    family: 'follows'
  },
  {
    interleave: [
      [
        {
          all: true
        }
      ],
      [
        {
          label: 'prezzy'
        },
        {
          sink: true
        }
      ]
    ]
  },
  {
    column: 'gwashington'
  }
];

//-
// As with an Filter#interleave filter, duplicate cells
// are possible, and appear in an unspecified mutual order. In this case we
// have a duplicates with multiple `gwashington` columns because one copy
// passed through the Filter#all filter while the other was
// passed through the Filter#label and sink. Note that one
// copy has label "prezzy" while the other does not.
//-

time(time)

Matches only cells with timestamps within the given range.

Parameters:
Name Type Description
time object

Start and End time Object

Example
const filter = [
  {
    time: {
      start: new Date('December 17, 2006 03:24:00'),
      end: new Date()
    }
  }
];

toProto()

If we detect multiple filters, we'll assume it's a chain filter and the execution of the filters will be the order in which they were specified.

value(value)

Matches only cells with values that satisfy the given regular expression. Note that, since cell values can contain arbitrary bytes, the '\C' escape sequence must be used if a true wildcard is desired. The '.' character will not match the new line character '\n', which may be present in a binary value.

Parameters:
Name Type Description
value string | Array.<string> | object

Value to filter cells

Example
const filter = [
  {
    value: /[0-9]/
  }
];

//-
// You can also provide a string (optionally containing regexp characters)
// for value filters.
//-
const filter = [
  {
    value: '1'
  }
];

//-
// You can also provide an array of strings if you wish to match against
// multiple values.
//-
const filter = [
  {
    value: ['1', '9']
  }
];

//-
// Or you can provide a Buffer or an array of Buffers if you wish to match
// against specfic binary value(s).
//-
const userInputedFaces = [Buffer.from('.|.'), Buffer.from(':-)')];
const filter = [
  {
    value: userInputedFaces
  }
];

//-
// <h4>Value Ranges</h4>
//
// Specifies a contiguous range of values.
//
// When the `start` bound is omitted it is interpreted as an empty string.
// When the `end` bound is omitted it is interpreted as Infinity.
//-
const filter = [
  {
    value: {
      start: '1',
      end: '9'
    }
  }
];

//-
// By default, both the `start` and `end` bounds are inclusive. You can
// override these by providing an object explicity stating whether or not it
// is `inclusive`.
//-
const filter = [
  {
    value: {
      start: {
        value: '1',
        inclusive: false
      },
      end: {
        value: '9',
        inclusive: false
      }
    }
  }
];

//-
// <h4>Strip Values</h4>
//
// Replaces each cell's value with an emtpy string.
//-
const filter = [
  {
    value: {
      strip: true
    }
  }
];