---
description: The add compute adds a number or another column's value to every value of a column.
date_published: 2026-08-13
date_modified: 2026-08-13
canonical_url: https://metricshub.org/community-connectors/develop/computes/add.html
---

# add (Compute)

On this Page

- [When To Use](#when-to-use)
- [Syntax](#syntax)
- [Properties](#properties)
- [Table Transformation Example](#table-transformation-example)
- [Recommended Pattern](#recommended-pattern)
- [Common Mistakes](#common-mistakes)
- [Community Examples](#community-examples)

## 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

```yaml
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

| Property | Required | Default | Description |
| --- | --- | --- | --- |
| `type` | Yes | None | `add`. |
| `column` | Yes | None | 1-based index of the column to update. Each value in this column is replaced by the result of the addition. |
| `value` | Yes | None | Operand added to the column value. Either a literal number (e.g. `100`) or a `$n` reference to another column of the same row (e.g. `$4` for the 4th column). |

## Table Transformation Example

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

#### Input

| DeviceId | ReadErrors | Wear | WriteErrors |
| --- | --- | --- | --- |
| disk0 | 12 | 3 | 5 |
| disk1 | 0 | 1 | 0 |

#### Result

| DeviceId | TotalErrors | Wear | WriteErrors |
| --- | --- | --- | --- |
| disk0 | 17 | 3 | 5 |
| disk1 | 0 | 1 | 0 |

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](https://github.com/metricshub/community-connectors/blob/main/src/main/connector/hardware/WinStorageSpaces/WinStorageSpaces.yaml)
- [WindowsProcess](https://github.com/metricshub/community-connectors/blob/main/src/main/connector/system/WindowsProcess/WindowsProcess.yaml)
- [MIB2-header](https://github.com/metricshub/community-connectors/blob/main/src/main/connector/hardware/MIB2-header/MIB2-header.yaml)

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
```