Indexes

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1.3.7.3 Indexes

As in C, Python indices are 0-based. For example, the first element in a list antlist would be antlist[0]:

CASA <113>: antlist=range(5)
CASA <114>: antlist
  Out[114]: [0, 1, 2, 3, 4]
CASA <115>: antlist[0]
  Out[115]: 0
CASA <116>: antlist[4]
  Out[116]: 4

CASA also uses 0-based indexing internally for elements in the Measurement Set (MS – the basic construct that contains visibility and/or single dish data; see Chapter 2). Thus, we will often talk about Field or Antenna “ID”s which will be start at 0. For example, the first field in an MS would have FIELD_ID==0 in the MSselect syntax, and can be addressed as be indexed as field=’0’ in most tasks, as well as by name field=’0137+331’ (assuming thats the name of the first field). You will see these indices in the MS summary from the task listobs.

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