extract (Compute)

When To Use

Use extract when a single column packs several pieces of information into one string — Model|Size, 2.5 GHz, Name,Instance — and you only need one of them. The compute splits the column value into sub-columns using the subSeparators characters and replaces the column, in place, with the sub-column selected by subColumn. All other columns and all rows are untouched.

For extracting a fixed-position slice of a string, see substring; for extracting a key="value" property from a WBEM object path, see extractPropertyFromWbemPath^[1].

Syntax

sources:
  diskInventory:
    type: commandLine
    commandLine: ${file::list-disks.sh}
    computes:
    # Column 5 contains "Model|Size"; keep only "Model"
    - type: extract
      column: 5
      subColumn: 1
      subSeparators: '|'

Properties

If column points past the end of a row, or a value in that column is missing, the compute logs a warning and leaves the whole table unchanged.

Table Transformation Example

With column: 5, subColumn: 1, subSeparators: '|':

Serialized, disk0;Seagate;ZC11ABC;ok;ST4000NM|4000 becomes disk0;Seagate;ZC11ABC;ok;ST4000NM.

Recommended Pattern

• Chain two extract computes to unpack a two-in-one column: first duplicateColumn, then extract sub-column 1 from the original and sub-column 2 from the copy (see IpmiTool, which splits Model|Size this way).
• Quote subSeparators whenever the character is meaningful in YAML ('|', '"', ':', ' ').
• Extract before numeric computes (multiply, divide): 2.5 GHz must become 2.5 before you can do arithmetic on it.

Common Mistakes

• Treating subSeparators as one multi-character delimiter: subSeparators: ', ' splits on comma and on space independently.
• Writing the property name as subSeparator (singular) — the correct property is subSeparators and a misspelled property is rejected by the schema.
• Forgetting that empty sub-parts count: with subSeparators: ':', the value a::b has sub-columns a, `` (empty) and b, so subColumn: 3 yields b.
• Expecting the split parts to be appended as new columns; extract replaces the original column with the single selected sub-part.

Community Examples

• IpmiTool^[2]
• Windows^[3]
• WBEMGenDiskNT^[4]

From IpmiTool (column 5 contains Model|Size; duplicate the column, then keep the model from the original and the size from the copy):

  # Duplicate the "Model" column because it is in the form of Model|Speed
  # Memory module;DeviceID;Entity ID;Vendor;Model|Speed;Model|Speed;SerialNumber;StatusArray;StatusInformation;AdditionalInformation1;
- type: duplicateColumn
  column: 5
  # Now extract "Model" from "Model|Size"
  # Memory module;DeviceID;Entity ID;Vendor;Model;Model|Speed;SerialNumber;StatusArray;StatusInformation;AdditionalInformation1;
- type: extract
  column: 5
  subColumn: 1
  subSeparators: '|'
  # Now extract "Size" from "Model|Size"
  # Memory module;DeviceID;Entity ID;Vendor;Model;Speed;SerialNumber;StatusArray;StatusInformation;AdditionalInformation1;
- type: extract
  column: 6
  subColumn: 2
  subSeparators: '|'