prev

Returns the value of a column from a row at a given offset before the current row in a serialized row set. A row set is serialized by the sort, top, top-hitters, or serialize operators; order-preserving operators (extend, project, where, ...) keep that property. Only valid in a serialized context.

prev(column, offset, default_value)

datatable(value:long)[
  1,
  2,
  3,
  4
]
| sort by value asc
| extend prev_value = prev(value)

datatable(value:long)[
  1,
  2,
  3,
  4
]
| sort by value asc
| extend prev_value = prev(value, 2, 0)