MSSelection.h

The MSSelection class represents a selection on a MeasurementSet (MS). This class is used in translating MS selections represented as selection items in the user interface, and for converting between MS selection and pure TaQL selection.

The purpose of this class is to provides a simple expression based selection mechanism to both the end-user and developer wishing to perform query operations over a measurement set. This is accomplished by abstracting the TaQL interface through an adapter/translation interface which converts STaQL (Simple Table Query Language) expressions into the equivalent table expression form, reducing the knowledge necessary to perform powerful query operations directly in TaQL.

The subexpressions available for performing a selection are as follows (a detailed syntax for each expression is also given below):

    antenna - Antenna STaQL expression
      antenna=ANTENNA.INDEX
      antenna='ANTENNA.NAME'
      antenna='ANTENNA.STATION'
      antenna=ANTENNA.INDEX : POL
      antenna=ANTENNA.INDEX : FEED POL
      antenna=ANTENNA.INDEX & ANTENNA.INDEX
      antenna=( ANTENNA.INDEX , ANTENNA.INDEX )
      antenna=( ANTENNA.INDEX - ANTENNA.INDEX )
      antenna=ANTENNA.INDEX & ANTENNA.INDEX : POL
      antenna=ANTENNA.INDEX : POL & ANTENNA.INDEX
      antenna=ANTENNA.INDEX : POL & ANTENNA.INDEX : POL
      antenna=( ANTENNA.INDEX , ANTENNA.INDEX ) : POL
      antenna=( ANTENNA.INDEX - ANTENNA.INDEX ) : POL
      antenna=ANTENNA.INDEX & *
      antenna=ANTENNA.NAME & *
      antenna=ANTENNA.NAME *
      antenna=[antennaexpr], [...]
    corr    - Correlator STaQL expression
      corr='RR'
      corr='RL'
      corr='LR'
      corr='LL'
      corr='XX'
      corr='XY'
      corr='YX'
      corr='YY'
      corr='I'
      corr='Q'
      corr='U'
      corr='V'
      corr='P'
      corr='Q'
      corr=[correxpr], [...]
    field   - Field STaQL expression
      field=FIELD.INDEX
      field='FIELD.NAME'
      field='FIELD.CODE'
      field='SOURCE.NAME'
      field='SOURCE.CODE'
      field=< FIELD.INDEX
      field=> FIELD.INDEX
      field=FIELD.INDEX - FIELD.INDEX
      field=FIELD.NAME *
      field=* FIELD.NAME
      field=[fieldexpr], [...]
    spw     - SPW STaQL expression
      spw=SPW.INDEX
      spw=SPW.NAME
      spw=SPW.INDEX : VALUE / VALUE / VALUE / VALUE
      spw=SPW.INDEX : VALUE - VALUE
      spw=SPW.INDEX : VALUE - VALUE UNIT
      spw=SPW.INDEX : ( VALUE , VALUE , ... )
      spw=SPW.INDEX : ( VALUE , VALUE , ... ) UNIT
      spw=[spwexpr], [...]
    scan    - Scan STaQL expression
      =SCAN.INDEX
      =SCAN.INDEX - SCAN.INDEX
      =[scanexpr], [...]
    time    - Time STaQL expression
      time='YYYY/MM/DD/HH:MM:SS.sss'
      time='ddd/HH:MM:SS.sss'
      time='< YYYY/MM/DD/HH:MM:SS.sss'
      time='> YYYY/MM/DD/HH:MM:SS.sss'
      time='YYYY/MM/DD/HH:MM:SS.sss - YYYY/MM/DD/HH:MM:SS.sss'
      time='YYYY[/MM][/DD][/HH][:MM][:SS][.sss]'
      time='ddd[/HH][:MM][:SS][.sss]'
      time=[timeexpr], [...]
    uvdist  - UV Distribution STaQL expression
      uvdist='< VALUE UNIT'
      uvdist='> VALUE UNIT'
      uvdist='VALUE - VALUE UNIT'
      uvdist='VALUE UNIT : PERCENTAGE %'
      uvdist=[uvdistexpr], [range]
    taql    - TaQL expression
      taql=[taqlexpr]

The subexpressions are interpreted in the order which they were set, with an AND between the results of each subexpression.

For a complete list of the STaQL interface refer to: Data Selection

Example

    // Create a MS and a MS selection
    MeasurementSet ms(msName);
    MSSelection select;
    // Setup any subexpressions of interest directly
    // (or optionally send this information through a Record)
    select.setFieldExpr("0,1");
    select.setSpwExpr(">0");
    // Create a table expression over a MS representing the selection
    TableExprNode node = select.toTableExprNode(&ms);
    // Optionally create a table and new MS based on this node
    Table tablesel(ms.tableName(), Table::Update);
    MeasurementSet mssel(tablesel(node, node.nrow()));