add (Compute)

When To Use

Use add to perform an addition on every value of one column, row by row. The operand is either a literal number or, with the $n syntax, the value of another column of the same row, which makes add the standard way to sum two counters into one (e.g. read errors + write errors = total errors, inbound + outbound traffic = total traffic). The column values must be numeric.

Syntax

sources:
  diskErrors:
    type: wmi
    namespace: root\Microsoft\Windows\Storage
    query: SELECT DeviceId,ReadErrorsTotal,Wear,WriteErrorsTotal FROM MSFT_StorageReliabilityCounter
    computes:
    # TotalErrors = ReadErrors + WriteErrors
    - type: add
      column: 2
      value: $4

Properties

Table Transformation Example

With column: 2 and value: $4, column 2 of each row becomes column 2 + column 4:

The operand column (here column 4) is left untouched; drop it later with keepColumns if it is no longer needed.

Recommended Pattern

• Use value: $n to sum two counter columns of the same row into a single metric column.
• Comment the expected column layout above the compute (# DeviceId;TotalErrors;Wear;WriteErrors) so later index changes are easy to review.
• Combine with multiply value: -1 when you need constant - column (negate, then add the constant), as no reversed-operand subtract exists.
• Add derived columns via the source query (select a field twice) rather than overwriting a value you still need downstream.

Common Mistakes

• Confusing column (the 1-based index that is overwritten) with value: $n (the operand that is only read).
• Forgetting that upstream computes (keepColumns, awk, json2Csv) may have renumbered the columns, so column and $n point to the wrong data.
• Applying add to a column that contains non-numeric text such as an empty string or a label.

Community Examples

• WinStorageSpaces^[1]
• WindowsProcess^[2]
• MIB2-header^[3]

From MIB2-header.yaml, accumulating the multicast and broadcast packet counters into the unicast packets column, included directly from the connector source:

  # Add MulticastPkts and BroadcastPkts to UnicastPackets
  # PortID;SpeedMBs;ReceivedBytes64;ReceivedUnicastPackets64;ifHCInMulticastPkts64;ifHCInBroadcastPkts64;TransmittedBytes64;TransmittedPackets64;ifHCOutMulticastPkts;ifHCOutBroadcastPkts;
- type: add
  column: 4
  value: $5
- type: add
  column: 4
  value: $6