documentationfilter_last¶
Type of operation: Filter
Description¶
Exclude rows from the input dataset that do not match the given predicate expression.
filter_last behaves identically to the verb filter except when the input is a Resource dataset.
See the documentation of filter for more details.
When the input is a Resource dataset, cell values may change over time for a given row. In this case, filter_last will
filter the rows based on their last value. When the input is a Resource dataset and the filter predicate refers to a column
which is time-mutable, then filter_last is not accelerable. See verb set_col_immutable
for more information on time-mutable and time-immutable columns. To make filter_last accelerable on a Resource dataset,
consider instead using ever with a frame or first using set_col_immutable. Consider also first converting the Resource
to an Event or Interval dataset using make_event or make_interval, upon which filter_last is accelerable.
Usage¶
filter_last predicate
Argument |
Type |
Optional |
Repeatable |
Restrictions |
|---|---|---|---|---|
predicate |
bool |
no |
no |
none |
Accelerable¶
filter_last is sometimes accelerable, depending on options used. A dataset that only uses accelerable verbs can be accelerated, making queries on the dataset respond faster.
Examples¶
filter_last string(status_code) ~ /^5.*/
Keep only rows where the status_code column, converted to string, starts with “5”.
For more simple examples, see the filter verb.
filter_last status="ON"
Where the input is a Resource dataset with a time-mutable column “status”, select the Resources whose last status during the query window was “ON”. This example is not accelerable.
filter_last server_id>100
Suppose the input is a Resource dataset describing many servers and how their statuses change over time. In this example, the primary key of the
input Resource is the column “server_id”, and this column is time-immutable. This example would select the servers whose server_id is greater
than 100. This example is accelerable because for a given server, its server_id cannot change over time.