Added a method to HeasarcClass that returns the number of rows in a named catalog

CHANGES.rst

@@ -54,6 +54,7 @@ heasarc
 - Add ``query_constraints`` to allow querying of different catalog columns. [#3403]
 - Add support for uploading tables when using TAP directly through ``query_tap``. [#3403]
 - Add automatic guessing for the data host in ``download_data``. [#3403]
+- Include method to count the number of rows in a specified table. [#3549]
 
 gaia
 ^^^^

astroquery/heasarc/core.py

@@ -958,5 +958,30 @@ def _s3_tree_download(client, bucket_name, path, local):
             path = key.replace(f's3://{self.S3_BUCKET}/', '')
             _s3_tree_download(self.s3_client, self.S3_BUCKET, path, location)
 
+    def count_rows(self, catalog: str) -> np.int64:
+        """
+        Returns the number of rows in the HEASARC-hosted catalog specified by
+        the `catalog` argument.
+
+        Parameters
+        ----------
+        catalog : `str`
+            The name of the catalog to query for a total number of rows. To list
+            the available catalogs, use
+            :meth:`~astroquery.heasarc.HeasarcClass.list_catalogs`.
+
+        Returns
+        -------
+        num_rows : `np.int64`
+            The total number of rows in the specified catalog.
+        """
+        # Send a query requesting a count of the number of rows in the
+        #  specified catalog.
+        count_return = self.query_tap(f"SELECT COUNT(*) FROM {catalog}")
+
+        # Extract an integer number of rows from the returned table.
+        num_rows = count_return["count"][0]
+        return num_rows
+
 
 Heasarc = HeasarcClass()

astroquery/heasarc/tests/test_heasarc_remote.py

@@ -273,6 +273,13 @@ def test_deprecated_pars(self, pars):
                 Heasarc.query_region(pos, mission="xmmmaster",
                                      **{keyword: value})
 
+    def test_row_count(self):
+        """Test the convenience method that uses ADQL's COUNT function to
+        return the number of rows in a catalog.
+        """
+        cat = "suzamaster"
+        assert Heasarc.count_rows(cat) == 3055
+
 
 @pytest.mark.remote_data
 class TestHeasarcBrowse:

docs/heasarc/heasarc.rst

@@ -422,6 +422,17 @@ in the XMM master catalog ``xmmmaster``:
     public_date     Public Date                              mjd
     ra              Right Ascension (Pointing Position)      degree
 
+Get Length Of Catalog
+---------------------
+To easily find out the number of rows in a catalog, use the `~astroquery.heasarc.HeasarcClass.count_rows`
+method. Here, for instance, we fetch the number of rows in the Suzaku 'master' observation table (``suzamaster``):
+
+.. doctest-remote-data::
+
+    >>> from astroquery.heasarc import Heasarc
+    >>> Heasarc.count_rows('suzamaster')
+    np.int64(3055)
+
 Reference/API
 =============