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Query

Getting Started

The basic usage of searching the MaNGA dataset with Marvin Queries is shown below. Queries allow you to perform searches filtering the sample on specific parameter conditions, as well as return additional desired parameters. Queries accept two basic keywords, search_filter and return_params.

You search the MaNGA dataset by constructing a string filter condition in a pseudo-SQL syntax of parameter operand value. You only need to care about constructing your filter or where clause, and Marvin will do the rest.

  • Condition I Want: find all galaxies with a redshift less than 0.1.
  • Constructor: Parameter: 'redshift (z or nsa.z)' + Operand: less than (<) + Value: 0.1
  • Marvin Filter Syntax: 'nsa.z < 0.1'
from marvin.tools.query import Query

# search for galaxies with an NSA redshift < 0.1
myfilter = 'nsa.z < 0.1'

# create a query
query = Query(search_filter=myfilter)

You can optionally return parameters using the return_params keyword, specified as a list of strings.

# return the galaxy RA and Dec as well
myfilter = 'nsa.z < 0.1'
myparams = ['cube.ra', 'cube.dec']

query = Query(search_filter=myfilter, return_params=myparams)

Queries contain a datamodel. You can access the datamodel used for a given query and data release with the datamodel attribute:

query.datamodel
<QueryDataModel release='MPL-5', n_groups=7, n_parameters=697, n_total=0>

To explore the query datamodel and see what parameters are available for returning and searching on, see the datamodel How To Guide <query-dm>

Finally, you can run the query with run. Queries produce results. Go to marvin-results to see how to manage your query results.

results = query.run()

Queries will always return a set of default parameters: the galaxy mangaid, plateifu, plate id, and ifu design name. Additionally, queries will always return any parameters used in your filter condition, plus any requested return parameters.

# see the returned columns
print(results.columns)
[u'cube.mangaid', u'cube.plate', u'cube.plateifu', u'ifu.name', 'cube.ra', 'cube.dec', 'nsa.z']

# look at the first row result
print(results.results[0])
ResultRow(mangaid=u'1-109394', plate=8082, plateifu=u'8082-9102', ifu_name=u'9102', ra=50.179936141, dec=-1.0022917898, z=0.0361073)

Using Query

Using the Query <query/query_using>

The Query Datamodel <datamodel/query_dm>

Returning Marvin objects <query/query_returntype>

Saving Queries <query/query_saving>

Reference/API

Class Inheritance Diagram

marvin.tools.query.Query

Class

marvin.tools.query.Query

Methods

marvin.tools.query.Query.run marvin.tools.query.Query.reset marvin.tools.query.Query.show marvin.tools.query.Query.save marvin.tools.query.Query.restore