excludeMatchingLines (Compute)

When To Use

Use excludeMatchingLines to drop unwanted rows from a source table: aggregate rows such as _Total in Windows performance counters, removable media in a disk listing, sensors reporting N/A, or devices with a size of 0. It is the table equivalent of grep -v: rows that match are discarded, all other rows pass through unchanged.

To do the opposite (keep only matching rows), use keepOnlyMatchingLines^[1].

Syntax

sources:
  physicalDisks:
    type: commandLine
    commandLine: ${file::diskpart-list.bat}
    computes:
    - type: excludeMatchingLines
      column: 4
      valueList: CD-ROM,DVD-ROM,Removable

Properties

Provide regExp, valueList, or both. When both are specified, both filters are applied one after the other: a row is removed if it matches the regExp or its value is in the valueList (only rows that pass both filters survive).

Table Transformation Example

With column: 4 and valueList: CD-ROM,DVD-ROM,Removable:

Recommended Pattern

• Exclude noise early in the computes pipeline (aggregate rows, N/A readings, zero-sized devices) so later computes and the mapping only see real hardware.
• Prefer valueList when the unwanted values are a fixed set of literals; use regExp for actual patterns, e.g. regExp: ^[0.]+$ in LibreHardwareMonitor to drop all-zero readings.
• Chain one excludeMatchingLines per column when you need to filter on several columns.

Common Mistakes

• Forgetting that regExp is unanchored: regExp: 5 removes every row whose column merely contains 5 — use valueList: 5 or regExp: ^5$ to remove exact values only.
• Expecting valueList entries to support wildcards; they are literal values only (the comparison is case-insensitive, though).
• Using excludeMatchingLines with a long value list when an anchored keepOnlyMatchingLines on the wanted values would be shorter and safer.
• Counting columns from 0: column is 1-based.

Community Examples

• DiskPart^[2]
• LibreHardwareMonitor^[3]
• Windows^[4]

From Windows (drops the _Total aggregate row of a performance counter table), included directly from the connector source:

- type: excludeMatchingLines
  column: 1
  regExp: _Total