Printing tables doesn't work correctly with 0-length array cells

Description

I have data in form of a list of dictionaries. Each dictionary contains some items with an integer value and some of these items set the length for 1 or more array values.

I am creating a Table using the rows attribute and feeding to it the list of dictionaries.

As long as I create a table until the first event with data in the array fields the table gets printed correctly. If I fill the table only with events with null array data (but the rest of the fields have something to show) I get an IndexError.

Expected behavior

The table should print fine also when there are only “bad” events

Actual behavior

I get the following error Traceback

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
File ~/Applications/mambaforge/envs/swgo/lib/python3.9/site-packages/IPython/core/formatters.py:707, in PlainTextFormatter.__call__(self, obj)
    700 stream = StringIO()
    701 printer = pretty.RepresentationPrinter(stream, self.verbose,
    702     self.max_width, self.newline,
    703     max_seq_length=self.max_seq_length,
    704     singleton_pprinters=self.singleton_printers,
    705     type_pprinters=self.type_printers,
    706     deferred_pprinters=self.deferred_printers)
--> 707 printer.pretty(obj)
    708 printer.flush()
    709 return stream.getvalue()

File ~/Applications/mambaforge/envs/swgo/lib/python3.9/site-packages/IPython/lib/pretty.py:410, in RepresentationPrinter.pretty(self, obj)
    407                         return meth(obj, self, cycle)
    408                 if cls is not object \
    409                         and callable(cls.__dict__.get('__repr__')):
--> 410                     return _repr_pprint(obj, self, cycle)
    412     return _default_pprint(obj, self, cycle)
    413 finally:

File ~/Applications/mambaforge/envs/swgo/lib/python3.9/site-packages/IPython/lib/pretty.py:778, in _repr_pprint(obj, p, cycle)
    776 """A pprint that just redirects to the normal repr function."""
    777 # Find newlines and replace them with p.break_()
--> 778 output = repr(obj)
    779 lines = output.splitlines()
    780 with p.group():

File ~/Applications/mambaforge/envs/swgo/lib/python3.9/site-packages/astropy/table/table.py:1534, in Table.__repr__(self)
   1533 def __repr__(self):
-> 1534     return self._base_repr_(html=False, max_width=None)

File ~/Applications/mambaforge/envs/swgo/lib/python3.9/site-packages/astropy/table/table.py:1516, in Table._base_repr_(self, html, descr_vals, max_width, tableid, show_dtype, max_lines, tableclass)
   1513 if tableid is None:
   1514     tableid = f'table{id(self)}'
-> 1516 data_lines, outs = self.formatter._pformat_table(
   1517     self, tableid=tableid, html=html, max_width=max_width,
   1518     show_name=True, show_unit=None, show_dtype=show_dtype,
   1519     max_lines=max_lines, tableclass=tableclass)
   1521 out = descr + '\n'.join(data_lines)
   1523 return out

File ~/Applications/mambaforge/envs/swgo/lib/python3.9/site-packages/astropy/table/pprint.py:589, in TableFormatter._pformat_table(self, table, max_lines, max_width, show_name, show_unit, show_dtype, html, tableid, tableclass, align)
    586 if col.info.name not in pprint_include_names:
    587     continue
--> 589 lines, outs = self._pformat_col(col, max_lines, show_name=show_name,
    590                                 show_unit=show_unit, show_dtype=show_dtype,
    591                                 align=align_)
    592 if outs['show_length']:
    593     lines = lines[:-1]

File ~/Applications/mambaforge/envs/swgo/lib/python3.9/site-packages/astropy/table/pprint.py:276, in TableFormatter._pformat_col(self, col, max_lines, show_name, show_unit, show_dtype, show_length, html, align)
    268 col_strs_iter = self._pformat_col_iter(col, max_lines, show_name=show_name,
    269                                        show_unit=show_unit,
    270                                        show_dtype=show_dtype,
    271                                        show_length=show_length,
    272                                        outs=outs)
    274 # Replace tab and newline with text representations so they display nicely.
    275 # Newline in particular is a problem in a multicolumn table.
--> 276 col_strs = [val.replace('\t', '\\t').replace('\n', '\\n') for val in col_strs_iter]
    277 if len(col_strs) > 0:
    278     col_width = max(len(x) for x in col_strs)

File ~/Applications/mambaforge/envs/swgo/lib/python3.9/site-packages/astropy/table/pprint.py:276, in <listcomp>(.0)
    268 col_strs_iter = self._pformat_col_iter(col, max_lines, show_name=show_name,
    269                                        show_unit=show_unit,
    270                                        show_dtype=show_dtype,
    271                                        show_length=show_length,
    272                                        outs=outs)
    274 # Replace tab and newline with text representations so they display nicely.
    275 # Newline in particular is a problem in a multicolumn table.
--> 276 col_strs = [val.replace('\t', '\\t').replace('\n', '\\n') for val in col_strs_iter]
    277 if len(col_strs) > 0:
    278     col_width = max(len(x) for x in col_strs)

File ~/Applications/mambaforge/envs/swgo/lib/python3.9/site-packages/astropy/table/pprint.py:493, in TableFormatter._pformat_col_iter(self, col, max_lines, show_name, show_unit, outs, show_dtype, show_length)
    491 else:
    492     try:
--> 493         yield format_col_str(idx)
    494     except ValueError:
    495         raise ValueError(
    496             'Unable to parse format string "{}" for entry "{}" '
    497             'in column "{}"'.format(col_format, col[idx],
    498                                     col.info.name))

File ~/Applications/mambaforge/envs/swgo/lib/python3.9/site-packages/astropy/table/pprint.py:481, in TableFormatter._pformat_col_iter.<locals>.format_col_str(idx)
    479     return format_func(col_format, col[(idx,) + multidim0])
    480 else:
--> 481     left = format_func(col_format, col[(idx,) + multidim0])
    482     right = format_func(col_format, col[(idx,) + multidim1])
    483     return f'{left} .. {right}'

File astropy/table/_column_mixins.pyx:74, in astropy.table._column_mixins._ColumnGetitemShim.__getitem__()

File astropy/table/_column_mixins.pyx:57, in astropy.table._column_mixins.base_getitem()

File astropy/table/_column_mixins.pyx:69, in astropy.table._column_mixins.column_getitem()

IndexError: index 0 is out of bounds for axis 1 with size 0
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
File ~/Applications/mambaforge/envs/swgo/lib/python3.9/site-packages/IPython/core/formatters.py:343, in BaseFormatter.__call__(self, obj)
    341     method = get_real_method(obj, self.print_method)
    342     if method is not None:
--> 343         return method()
    344     return None
    345 else:

File ~/Applications/mambaforge/envs/swgo/lib/python3.9/site-packages/astropy/table/table.py:1526, in Table._repr_html_(self)
   1525 def _repr_html_(self):
-> 1526     out = self._base_repr_(html=True, max_width=-1,
   1527                            tableclass=conf.default_notebook_table_class)
   1528     # Wrap <table> in <div>. This follows the pattern in pandas and allows
   1529     # table to be scrollable horizontally in VS Code notebook display.
   1530     out = f'<div>{out}</div>'

File ~/Applications/mambaforge/envs/swgo/lib/python3.9/site-packages/astropy/table/table.py:1516, in Table._base_repr_(self, html, descr_vals, max_width, tableid, show_dtype, max_lines, tableclass)
   1513 if tableid is None:
   1514     tableid = f'table{id(self)}'
-> 1516 data_lines, outs = self.formatter._pformat_table(
   1517     self, tableid=tableid, html=html, max_width=max_width,
   1518     show_name=True, show_unit=None, show_dtype=show_dtype,
   1519     max_lines=max_lines, tableclass=tableclass)
   1521 out = descr + '\n'.join(data_lines)
   1523 return out

File ~/Applications/mambaforge/envs/swgo/lib/python3.9/site-packages/astropy/table/pprint.py:589, in TableFormatter._pformat_table(self, table, max_lines, max_width, show_name, show_unit, show_dtype, html, tableid, tableclass, align)
    586 if col.info.name not in pprint_include_names:
    587     continue
--> 589 lines, outs = self._pformat_col(col, max_lines, show_name=show_name,
    590                                 show_unit=show_unit, show_dtype=show_dtype,
    591                                 align=align_)
    592 if outs['show_length']:
    593     lines = lines[:-1]

File ~/Applications/mambaforge/envs/swgo/lib/python3.9/site-packages/astropy/table/pprint.py:276, in TableFormatter._pformat_col(self, col, max_lines, show_name, show_unit, show_dtype, show_length, html, align)
    268 col_strs_iter = self._pformat_col_iter(col, max_lines, show_name=show_name,
    269                                        show_unit=show_unit,
    270                                        show_dtype=show_dtype,
    271                                        show_length=show_length,
    272                                        outs=outs)
    274 # Replace tab and newline with text representations so they display nicely.
    275 # Newline in particular is a problem in a multicolumn table.
--> 276 col_strs = [val.replace('\t', '\\t').replace('\n', '\\n') for val in col_strs_iter]
    277 if len(col_strs) > 0:
    278     col_width = max(len(x) for x in col_strs)

File ~/Applications/mambaforge/envs/swgo/lib/python3.9/site-packages/astropy/table/pprint.py:276, in <listcomp>(.0)
    268 col_strs_iter = self._pformat_col_iter(col, max_lines, show_name=show_name,
    269                                        show_unit=show_unit,
    270                                        show_dtype=show_dtype,
    271                                        show_length=show_length,
    272                                        outs=outs)
    274 # Replace tab and newline with text representations so they display nicely.
    275 # Newline in particular is a problem in a multicolumn table.
--> 276 col_strs = [val.replace('\t', '\\t').replace('\n', '\\n') for val in col_strs_iter]
    277 if len(col_strs) > 0:
    278     col_width = max(len(x) for x in col_strs)

File ~/Applications/mambaforge/envs/swgo/lib/python3.9/site-packages/astropy/table/pprint.py:493, in TableFormatter._pformat_col_iter(self, col, max_lines, show_name, show_unit, outs, show_dtype, show_length)
    491 else:
    492     try:
--> 493         yield format_col_str(idx)
    494     except ValueError:
    495         raise ValueError(
    496             'Unable to parse format string "{}" for entry "{}" '
    497             'in column "{}"'.format(col_format, col[idx],
    498                                     col.info.name))

File ~/Applications/mambaforge/envs/swgo/lib/python3.9/site-packages/astropy/table/pprint.py:481, in TableFormatter._pformat_col_iter.<locals>.format_col_str(idx)
    479     return format_func(col_format, col[(idx,) + multidim0])
    480 else:
--> 481     left = format_func(col_format, col[(idx,) + multidim0])
    482     right = format_func(col_format, col[(idx,) + multidim1])
    483     return f'{left} .. {right}'

File astropy/table/_column_mixins.pyx:74, in astropy.table._column_mixins._ColumnGetitemShim.__getitem__()

File astropy/table/_column_mixins.pyx:57, in astropy.table._column_mixins.base_getitem()

File astropy/table/_column_mixins.pyx:69, in astropy.table._column_mixins.column_getitem()

IndexError: index 0 is out of bounds for axis 1 with size 0

Steps to Reproduce

This is an example dataset: field “B” set the length of field “C”, so the first 2 events have an empty array in “C”

events = [{"A":0,"B":0, "C":np.array([], dtype=np.uint64)},
          {"A":1,"B":0, "C":np.array([], dtype=np.uint64)},
          {"A":2,"B":2, "C":np.array([0,1], dtype=np.uint64)}]

Showing just the first event prints the column names as a column,

Printing the first 2 throws the Traceback above QTable(rows=events[:2])

Plotting all 3 events works

System Details

macOS-11.7-x86_64-i386-64bit Python 3.9.13 | packaged by conda-forge | (main, May 27 2022, 17:00:52) [Clang 13.0.1 ] Numpy 1.23.3 pyerfa 2.0.0.1 astropy 5.1 Scipy 1.9.1 Matplotlib 3.6.0

[taldcroft]

The last example you show is expected. The rows=.. requires a list of rows and you passed a single dict. This is equivalent to Table(rows=["a", "b", "c"]) (three rows of a single column). There could be better input validation, but what you want to pass is rows=events[0:1].

[taldcroft]

See #13838 for a fix to the root cause problem. You will still need to be careful about creating an object array with all empty lists.