Start on implementing and testing NetCDFTimeIndex

Author: spencerkclark

xarray/core/netcdftimeindex.py

@@ -0,0 +1,180 @@
+import re
+from datetime import timedelta
+
+import numpy as np
+import pandas as pd
+
+from pandas.lib import isscalar
+
+
+def named(name, pattern):
+    return '(?P<' + name + '>' + pattern + ')'
+
+
+def optional(x):
+    return '(?:' + x + ')?'
+
+
+def trailing_optional(xs):
+    if not xs:
+        return ''
+    return xs[0] + optional(trailing_optional(xs[1:]))
+
+
+def build_pattern(date_sep='\-', datetime_sep='T', time_sep='\:'):
+    pieces = [(None, 'year', '\d{4}'),
+              (date_sep, 'month', '\d{2}'),
+              (date_sep, 'day', '\d{2}'),
+              (datetime_sep, 'hour', '\d{2}'),
+              (time_sep, 'minute', '\d{2}'),
+              (time_sep, 'second', '\d{2}' + optional('\.\d+'))]
+    pattern_list = []
+    for sep, name, sub_pattern in pieces:
+        pattern_list.append((sep if sep else '') + named(name, sub_pattern))
+        # TODO: allow timezone offsets?
+    return '^' + trailing_optional(pattern_list) + '$'
+
+
+def parse_iso8601(datetime_string):
+    basic_pattern = build_pattern(date_sep='', time_sep='')
+    extended_pattern = build_pattern()
+    patterns = [basic_pattern, extended_pattern]
+    for pattern in patterns:
+        match = re.match(pattern, datetime_string)
+        if match:
+            return match.groupdict()
+    raise ValueError('no ISO-8601 match for string: %s' % datetime_string)
+
+
+def _parse_iso8601_with_reso(date_type, timestr):
+    default = date_type(1, 1, 1)
+    result = parse_iso8601(timestr)
+    replace = {}
+
+    for attr in ['year', 'month', 'day', 'hour', 'minute', 'second']:
+        value = result.get(attr, None)
+        if value is not None:
+            replace[attr] = int(value)
+            resolution = attr
+
+    return default.replace(**replace), resolution
+
+
+def _parsed_string_to_bounds(date_type, resolution, parsed):
+    if resolution == 'year':
+        return (date_type(parsed.year, 1, 1),
+                date_type(parsed.year + 1, 1, 1) - timedelta(microseconds=1))
+    if resolution == 'month':
+        if parsed.month == 12:
+            end = date_type(parsed.year + 1, 1, 1) - timedelta(microseconds=1)
+        else:
+            end = (date_type(parsed.year, parsed.month + 1, 1) -
+                   timedelta(microseconds=1))
+        return date_type(parsed.year, parsed.month, 1), end
+    if resolution == 'day':
+        start = date_type(parsed.year, parsed.month, parsed.day)
+        return start, start + timedelta(days=1, microseconds=-1)
+    if resolution == 'hour':
+        start = date_type(parsed.year, parsed.month, parsed.day, parsed.hour)
+        return start, start + timedelta(hours=1, microseconds=-1)
+    if resolution == 'minute':
+        start = date_type(parsed.year, parsed.month, parsed.day, parsed.hour,
+                          parsed.minute)
+        return start, start + timedelta(minutes=1, microseconds=-1)
+    if resolution == 'second':
+        start = date_type(parsed.year, parsed.month, parsed.day, parsed.hour,
+                          parsed.minute, parsed.second)
+        return start, start + timedelta(seconds=1, microseconds=-1)
+    else:
+        raise KeyError
+
+
+def get_date_field(datetimes, field):
+    return [getattr(date, field) for date in datetimes]
+
+
+def _field_accessor(name, docstring=None):
+    def f(self):
+        return get_date_field(self._data, name)
+
+    f.__name__ = name
+    f.__doc__ = docstring
+    return property(f)
+
+
+def get_date_type(self):
+    return type(self._data[0])
+
+
+class NetCDFTimeIndex(pd.Index):
+    def __new__(cls, data):
+        result = object.__new__(cls)
+        result._data = np.array(data)
+        return result
+
+    year = _field_accessor('year', 'The year of the datetime')
+    month = _field_accessor('month', 'The month of the datetime')
+    day = _field_accessor('day', 'The days of the datetime')
+    hour = _field_accessor('hour', 'The hours of the datetime')
+    minute = _field_accessor('minute', 'The minutes of the datetime')
+    second = _field_accessor('second', 'The seconds of the datetime')
+    microsecond = _field_accessor('microsecond',
+                                  'The microseconds of the datetime')
+    date_type = property(get_date_type)
+
+    def _partial_date_slice(self, resolution, parsed,
+                            use_lhs=True, use_rhs=True):
+        start, end = _parsed_string_to_bounds(self.date_type, resolution,
+                                              parsed)
+        lhs_mask = (self._data >= start) if use_lhs else True
+        rhs_mask = (self._data <= end) if use_rhs else True
+        return (lhs_mask & rhs_mask).nonzero()[0]
+
+    def _get_string_slice(self, key, use_lhs=True, use_rhs=True):
+        parsed, resolution = _parse_iso8601_with_reso(self.date_type, key)
+        loc = self._partial_date_slice(resolution, parsed, use_lhs, use_rhs)
+        return loc
+
+    def get_loc(self, key, method=None, tolerance=None):
+        if isinstance(key, pd.compat.string_types):
+            result = self._get_string_slice(key)
+            # Prevents problem with __contains__ if key corresponds to only
+            # the first element in index (if we leave things as a list,
+            # np.any([0]) is False).
+            # Also coerces things to scalar coords in xarray if possible,
+            # which is consistent with the behavior with a DatetimeIndex.
+            if len(result) == 1:
+                return result[0]
+            else:
+                return result
+        else:
+            return pd.Index.get_loc(self, key, method=method,
+                                    tolerance=tolerance)
+
+    def _maybe_cast_slice_bound(self, label, side, kind):
+        if isinstance(label, pd.compat.string_types):
+            parsed, resolution = _parse_iso8601_with_reso(self.date_type,
+                                                          label)
+            start, end = _parsed_string_to_bounds(self.date_type, resolution,
+                                                  parsed)
+            if self.is_monotonic_decreasing and len(self):
+                return end if side == 'left' else start
+            return start if side == 'left' else end
+        else:
+            return label
+
+    # TODO: Add ability to use integer range outside of iloc?
+    # e.g. series[1:5].
+    def get_value(self, series, key):
+        if not isinstance(key, slice):
+            return series.iloc[self.get_loc(key)]
+        else:
+            return series.iloc[self.slice_indexer(
+                key.start, key.stop, key.step)]
+
+    def __contains__(self, key):
+        try:
+            result = self.get_loc(key)
+            return isscalar(result) or type(result) == slice or np.any(result)
+        except (KeyError, TypeError, ValueError):
+            return False