Debugging

DataFrame visualization depends on graphviz and the graphviz package for Python.

>>> df = iris.groupby('name').agg(id=iris.sepalwidth.sum())
>>> df = df[df.name, df.id + 3]
>>> df.visualize()

The computation process shows that PyODPS DataFrame combines the groupby operation and the column filtering operation.

>>> df = iris.groupby('name').agg(id=iris.sepalwidth.sum()).cache()
>>> df2 = df[df.name, df.id + 3]
>>> df2.visualize()

The entire execution process runs in two steps because a cache operation is performed.

Call the compile method to view compiled results of SQL statements at the MaxCompute SQL backend.

>>> df = iris.groupby('name').agg(sepalwidth=iris.sepalwidth.max())
>>> df.compile()
Stage 1:

SQL compiled:

SELECT
  t1.`name`,
  MAX(t1.`sepalwidth`) AS `sepalwidth`
FROM test_pyodps_dev.`pyodps_iris` t1
GROUP BY
  t1.`name`

If you use MaxCompute tables as the sources for DataFrame objects, the system does not compile or perform some operations at the MaxCompute SQL backend. Instead, the system uses the MaxCompute Tunnel service to download data. This way, the system does not need to wait for the MaxCompute SQL backend to schedule download tasks. This allows you to download small amounts of data from MaxCompute to a local directory and use the pandas computation backend to compile and debug code. You can perform the following debugging operations:

• Select all or some rows of data from a non-partitioned table, or filter the column data, and then calculate the number of specified rows. The column filtering operation does not compute column values.
• Select all or some rows of data from all or the first several partition columns that are specified in a partitioned table, or filter the column data, and then calculate the number of the specified rows.

Assume that the iris DataFrame object uses a non-partitioned MaxCompute table as the source. The following operation uses the MaxCompute Tunnel service to download data:

>>> iris.count()
>>> iris['name', 'sepalwidth'][:10]

>>> df[:10]
>>> df[df.ds == '20160808']['f0', 'f1']
>>> df[(df.ds == '20160808') & (df.hh == 3)][:10]
>>> df[(df.ds == '20160808') & (df.hh == 3) & (df.mm == 15)]

>>> DEBUG = True
>>> if DEBUG:
>>> df = iris[:100].to_pandas(wrap=True)
>>> else:
>>> df = iris