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column.py
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column.py
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#!/usr/bin/env python3
#
# Copyright (c) 2012-2022 Snowflake Computing Inc. All rights reserved.
#
from typing import Iterable, Optional, Union
import snowflake.snowpark
from snowflake.snowpark._internal.analyzer.analyzer_utils import quote_name
from snowflake.snowpark._internal.analyzer.binary_expression import (
Add,
And,
BitwiseAnd,
BitwiseOr,
BitwiseXor,
Divide,
EqualNullSafe,
EqualTo,
GreaterThan,
GreaterThanOrEqual,
LessThan,
LessThanOrEqual,
Multiply,
NotEqualTo,
Or,
Pow,
Remainder,
Subtract,
)
from snowflake.snowpark._internal.analyzer.expression import (
CaseWhen,
Collate,
Expression,
InExpression,
Like,
Literal,
MultipleExpression,
NamedExpression,
RegExp,
ScalarSubquery,
Star,
SubfieldInt,
SubfieldString,
UnresolvedAttribute,
WithinGroup,
)
from snowflake.snowpark._internal.analyzer.sort_expression import (
Ascending,
Descending,
NullsFirst,
NullsLast,
SortOrder,
)
from snowflake.snowpark._internal.analyzer.unary_expression import (
Alias,
Cast,
IsNaN,
IsNotNull,
IsNull,
Not,
UnaryMinus,
UnresolvedAlias,
)
from snowflake.snowpark._internal.type_utils import (
VALID_PYTHON_TYPES_FOR_LITERAL_VALUE,
ColumnOrLiteral,
ColumnOrLiteralStr,
ColumnOrName,
ColumnOrSqlExpr,
LiteralType,
type_string_to_type_object,
)
from snowflake.snowpark._internal.utils import parse_positional_args_to_list
from snowflake.snowpark.types import DataType
from snowflake.snowpark.window import Window, WindowSpec
def _to_col_if_lit(
col: Union[ColumnOrLiteral, "snowflake.snowpark.DataFrame"], func_name: str
) -> "Column":
if isinstance(col, (Column, snowflake.snowpark.DataFrame, list, tuple, set)):
return col
elif isinstance(col, VALID_PYTHON_TYPES_FOR_LITERAL_VALUE):
return Column(Literal(col))
else: # pragma: no cover
raise TypeError(
f"'{func_name}' expected Column, DataFrame, Iterable or LiteralType, got: {type(col)}"
)
def _to_col_if_sql_expr(col: ColumnOrSqlExpr, func_name: str) -> "Column":
if isinstance(col, Column):
return col
elif isinstance(col, str):
return Column._expr(col)
else:
raise TypeError(
f"'{func_name}' expected Column or str as SQL expression, got: {type(col)}"
)
def _to_col_if_str(col: ColumnOrName, func_name: str) -> "Column":
if isinstance(col, Column):
return col
elif isinstance(col, str):
return Column(col)
else:
raise TypeError(
f"'{func_name.upper()}' expected Column or str, got: {type(col)}"
)
def _to_col_if_str_or_int(col: Union[ColumnOrName, int], func_name: str) -> "Column":
if isinstance(col, Column):
return col
elif isinstance(col, str):
return Column(col)
elif isinstance(col, int):
return Column(Literal(col))
else: # pragma: no cover
raise TypeError(
f"'{func_name.upper()}' expected Column, int or str, got: {type(col)}"
)
class Column:
"""Represents a column or an expression in a :class:`DataFrame`.
To access a Column object that refers a column in a :class:`DataFrame`, you can:
- Use the column name.
- Use the :func:`functions.col` function.
- Use the :func:`DataFrame.col` method.
- Use the index operator ``[]`` on a dataframe object with a column name.
- Use the dot operator ``.`` on a dataframe object with a column name.
>>> from snowflake.snowpark.functions import col
>>> df = session.create_dataframe([["John", 1], ["Mike", 11]], schema=["name", "age"])
>>> df.select("name").collect()
[Row(NAME='John'), Row(NAME='Mike')]
>>> df.select(col("name")).collect()
[Row(NAME='John'), Row(NAME='Mike')]
>>> df.select(df.col("name")).collect()
[Row(NAME='John'), Row(NAME='Mike')]
>>> df.select(df["name"]).collect()
[Row(NAME='John'), Row(NAME='Mike')]
>>> df.select(df.name).collect()
[Row(NAME='John'), Row(NAME='Mike')]
Snowflake object identifiers, including column names, may or may not be case sensitive depending on a set of rules.
Refer to `Snowflake Object Identifier Requirements <https://docs.snowflake.com/en/sql-reference/identifiers-syntax.html>`_ for details.
When you use column names with a DataFrame, you should follow these rules.
The returned column names after a DataFrame is evaluated follow the case-sensitivity rules too.
The above ``df`` was created with column name "name" while the returned column name after ``collect()`` was called became "NAME".
It's because the column is regarded as ignore-case so the Snowflake database returns the upper case.
To create a Column object that represents a constant value, use :func:`snowflake.snowpark.functions.lit`:
>>> from snowflake.snowpark.functions import lit
>>> df.select(col("name"), lit("const value").alias("literal_column")).collect()
[Row(NAME='John', LITERAL_COLUMN='const value'), Row(NAME='Mike', LITERAL_COLUMN='const value')]
This class also defines utility functions for constructing expressions with Columns.
Column objects can be built with the operators, summarized by operator precedence,
in the following table:
============================================== ==============================================
Operator Description
============================================== ==============================================
``x[index]`` Index operator to get an item out of a Snowflake ARRAY or OBJECT
``**`` Power
``-x``, ``~x`` Unary minus, unary not
``*``, ``/``, ``%`` Multiply, divide, remainder
``+``, ``-`` Plus, minus
``&`` And
``|`` Or
``==``, ``!=``, ``<``, ``<=``, ``>``, ``>=`` Equal to, not equal to, less than, less than or equal to, greater than, greater than or equal to
============================================== ==============================================
The following examples demonstrate how to use Column objects in expressions:
>>> df = session.create_dataframe([[20, 5], [1, 2]], schema=["a", "b"])
>>> df.filter((col("a") == 20) | (col("b") <= 10)).collect() # use parentheses before and after the | operator.
[Row(A=20, B=5), Row(A=1, B=2)]
>>> df.filter((df["a"] + df.b) < 10).collect()
[Row(A=1, B=2)]
>>> df.select((col("b") * 10).alias("c")).collect()
[Row(C=50), Row(C=20)]
When you use ``|``, ``&``, and ``~`` as logical operators on columns, you must always enclose column expressions
with parentheses as illustrated in the above example, because their order precedence is higher than ``==``, ``<``, etc.
Do not use ``and``, ``or``, and ``not`` logical operators on column objects, for instance, ``(df.col1 > 1) and (df.col2 > 2)`` is wrong.
The reason is Python doesn't have a magic method, or dunder method for them.
It will raise an error and tell you to use ``|``, ``&`` or ``~``, for which Python has magic methods.
A side effect is ``if column:`` will raise an error because it has a hidden call to ``bool(a_column)``, like using the ``and`` operator.
Use ``if a_column is None:`` instead.
To access elements of a semi-structured Object and Array, use ``[]`` on a Column object:
>>> from snowflake.snowpark.types import StringType, IntegerType
>>> df_with_semi_data = session.create_dataframe([[{"k1": "v1", "k2": "v2"}, ["a0", 1, "a2"]]], schema=["object_column", "array_column"])
>>> df_with_semi_data.select(df_with_semi_data["object_column"]["k1"].alias("k1_value"), df_with_semi_data["array_column"][0].alias("a0_value"), df_with_semi_data["array_column"][1].alias("a1_value")).collect()
[Row(K1_VALUE='"v1"', A0_VALUE='"a0"', A1_VALUE='1')]
>>> # The above two returned string columns have JSON literal values because children of semi-structured data are semi-structured.
>>> # The next line converts JSON literal to a string
>>> df_with_semi_data.select(df_with_semi_data["object_column"]["k1"].cast(StringType()).alias("k1_value"), df_with_semi_data["array_column"][0].cast(StringType()).alias("a0_value"), df_with_semi_data["array_column"][1].cast(IntegerType()).alias("a1_value")).collect()
[Row(K1_VALUE='v1', A0_VALUE='a0', A1_VALUE=1)]
This class has methods for the most frequently used column transformations and operators. Module :mod:`snowflake.snowpark.functions` defines many functions to transform columns.
"""
def __init__(self, expr: Union[str, Expression]) -> None:
if isinstance(expr, str):
if expr == "*":
self._expression = Star([])
else:
self._expression = UnresolvedAttribute(quote_name(expr))
elif isinstance(expr, Expression):
self._expression = expr
else: # pragma: no cover
raise TypeError("Column constructor only accepts str or expression.")
def __getitem__(self, field: Union[str, int]) -> "Column":
"""Accesses an element of ARRAY column by ordinal position, or an element of OBJECT column by key."""
if isinstance(field, str):
return Column(SubfieldString(self._expression, field))
elif isinstance(field, int):
return Column(SubfieldInt(self._expression, field))
else:
raise TypeError(f"Unexpected item type: {type(field)}")
# overload operators
def __eq__(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
"""Equal to."""
right = Column._to_expr(other)
return Column(EqualTo(self._expression, right))
def __ne__(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
"""Not equal to."""
right = Column._to_expr(other)
return Column(NotEqualTo(self._expression, right))
def __gt__(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
"""Greater than."""
return Column(GreaterThan(self._expression, Column._to_expr(other)))
def __lt__(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
"""Less than."""
return Column(LessThan(self._expression, Column._to_expr(other)))
def __ge__(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
"""Greater than or equal to."""
return Column(GreaterThanOrEqual(self._expression, Column._to_expr(other)))
def __le__(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
"""Less than or equal to."""
return Column(LessThanOrEqual(self._expression, Column._to_expr(other)))
def __add__(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
"""Plus."""
return Column(Add(self._expression, Column._to_expr(other)))
def __radd__(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
return Column(Add(Column._to_expr(other), self._expression))
def __sub__(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
"""Minus."""
return Column(Subtract(self._expression, Column._to_expr(other)))
def __rsub__(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
return Column(Subtract(Column._to_expr(other), self._expression))
def __mul__(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
"""Multiply."""
return Column(Multiply(self._expression, Column._to_expr(other)))
def __rmul__(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
return Column(Multiply(Column._to_expr(other), self._expression))
def __truediv__(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
"""Divide."""
return Column(Divide(self._expression, Column._to_expr(other)))
def __rtruediv__(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
return Column(Divide(Column._to_expr(other), self._expression))
def __mod__(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
"""Reminder."""
return Column(Remainder(self._expression, Column._to_expr(other)))
def __rmod__(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
return Column(Remainder(Column._to_expr(other), self._expression))
def __pow__(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
"""Power."""
return Column(Pow(self._expression, Column._to_expr(other)))
def __rpow__(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
return Column(Pow(Column._to_expr(other), self._expression))
def __bool__(self) -> bool:
raise TypeError(
"Cannot convert a Column object into bool: please use '&' for 'and', '|' for 'or', "
"'~' for 'not' if you're building DataFrame filter expressions. For example, use df.filter((col1 > 1) & (col2 > 2)) instead of df.filter(col1 > 1 and col2 > 2)."
)
def __iter__(self) -> None:
raise TypeError(
"Column is not iterable. This error can occur when you use the Python built-ins for sum, min and max. Please make sure you use the corresponding function from snowflake.snowpark.functions."
)
def __round__(self, n=None):
raise TypeError(
"Column cannot be rounded. This error can occur when you use the Python built-in round. Please make sure you use the snowflake.snowpark.functions.round function instead."
)
def in_(
self,
*vals: Union[
LiteralType,
Iterable[LiteralType],
"snowflake.snowpark.DataFrame",
],
) -> "Column":
"""Returns a conditional expression that you can pass to the :meth:`DataFrame.filter`
or where :meth:`DataFrame.where` to perform the equivalent of a WHERE ... IN query
with a specified list of values. You can also pass this to a
:meth:`DataFrame.select` call.
The expression evaluates to true if the value in the column is one of the values in
a specified sequence.
For example, the following code returns a DataFrame that contains the rows where
the column "a" contains the value 1, 2, or 3. This is equivalent to
``SELECT * FROM table WHERE a IN (1, 2, 3)``.
:meth:`isin` is an alias for :meth:`in_`.
Examples::
>>> from snowflake.snowpark.functions import lit
>>> df = session.create_dataframe([[1, "x"], [2, "y"] ,[4, "z"]], schema=["a", "b"])
>>> # Basic example
>>> df.filter(df["a"].in_(lit(1), lit(2), lit(3))).collect()
[Row(A=1, B='x'), Row(A=2, B='y')]
>>> # Check in membership for a DataFrame that has a single column
>>> df_for_in = session.create_dataframe([[1], [2] ,[3]], schema=["col1"])
>>> df.filter(df["a"].in_(df_for_in)).sort(df["a"].asc()).collect()
[Row(A=1, B='x'), Row(A=2, B='y')]
>>> # Use in with a select method call
>>> df.select(df["a"].in_(lit(1), lit(2), lit(3)).alias("is_in_list")).collect()
[Row(IS_IN_LIST=True), Row(IS_IN_LIST=True), Row(IS_IN_LIST=False)]
Args:
vals: The values, or a :class:`DataFrame` instance to use to check for membership against this column.
"""
cols = parse_positional_args_to_list(*vals)
cols = [_to_col_if_lit(col, "in_") for col in cols]
column_count = (
len(self._expression.expressions)
if isinstance(self._expression, MultipleExpression)
else 1
)
def value_mapper(value):
if isinstance(value, (tuple, set, list)):
if len(value) == column_count:
return MultipleExpression([Column._to_expr(v) for v in value])
else:
raise ValueError(
f"The number of values {len(value)} does not match the number of columns {column_count}."
)
elif isinstance(value, snowflake.snowpark.DataFrame):
if len(value.schema.fields) == column_count:
return ScalarSubquery(value._plan)
else:
raise ValueError(
f"The number of values {len(value.schema.fields)} does not match the number of columns {column_count}."
)
else:
return Column._to_expr(value)
value_expressions = [value_mapper(col) for col in cols]
if len(cols) != 1 or not isinstance(value_expressions[0], ScalarSubquery):
def validate_value(value_expr: Expression):
if isinstance(value_expr, Literal):
return
elif isinstance(value_expr, MultipleExpression):
for expr in value_expr.expressions:
validate_value(expr)
return
else:
raise TypeError(
f"'{type(value_expr)}' is not supported for the values parameter of the function "
f"in(). You must either specify a sequence of literals or a DataFrame that "
f"represents a subquery."
)
for ve in value_expressions:
validate_value(ve)
return Column(InExpression(self._expression, value_expressions))
def between(
self,
lower_bound: Union[ColumnOrLiteral, Expression],
upper_bound: Union[ColumnOrLiteral, Expression],
) -> "Column":
"""Between lower bound and upper bound."""
return (Column._to_expr(lower_bound) <= self) & (
self <= Column._to_expr(upper_bound)
)
def bitand(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
"""Bitwise and."""
return Column(BitwiseAnd(Column._to_expr(other), self._expression))
def bitor(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
"""Bitwise or."""
return Column(BitwiseOr(Column._to_expr(other), self._expression))
def bitxor(self, other: Union[ColumnOrLiteral, Expression]) -> "Column":
"""Bitwise xor."""
return Column(BitwiseXor(Column._to_expr(other), self._expression))
def __neg__(self) -> "Column":
"""Unary minus."""
return Column(UnaryMinus(self._expression))
def equal_null(self, other: "Column") -> "Column":
"""Equal to. You can use this for comparisons against a null value."""
return Column(EqualNullSafe(self._expression, Column._to_expr(other)))
def equal_nan(self) -> "Column":
"""Is NaN."""
return Column(IsNaN(self._expression))
def is_null(self) -> "Column":
"""Is null."""
return Column(IsNull(self._expression))
def is_not_null(self) -> "Column":
"""Is not null."""
return Column(IsNotNull(self._expression))
# `and, or, not` cannot be overloaded in Python, so use bitwise operators as boolean operators
def __and__(self, other: "Column") -> "Column":
"""And."""
return Column(And(self._expression, Column._to_expr(other)))
def __rand__(self, other: "Column") -> "Column":
return Column(And(Column._to_expr(other), self._expression)) # pragma: no cover
def __or__(self, other: "Column") -> "Column":
"""Or."""
return Column(Or(self._expression, Column._to_expr(other)))
def __ror__(self, other: "Column") -> "Column":
return Column(And(Column._to_expr(other), self._expression)) # pragma: no cover
def __invert__(self) -> "Column":
"""Unary not."""
return Column(Not(self._expression))
def _cast(self, to: Union[str, DataType], try_: bool = False) -> "Column":
if isinstance(to, str):
to = type_string_to_type_object(to)
return Column(Cast(self._expression, to, try_))
def cast(self, to: Union[str, DataType]) -> "Column":
"""Casts the value of the Column to the specified data type.
It raises an error when the conversion can not be performed.
"""
return self._cast(to, False)
def try_cast(self, to: Union[str, DataType]) -> "Column":
"""Tries to cast the value of the Column to the specified data type.
It returns a NULL value instead of raising an error when the conversion can not be performed.
"""
return self._cast(to, True)
def desc(self) -> "Column":
"""Returns a Column expression with values sorted in descending order."""
return Column(SortOrder(self._expression, Descending()))
def desc_nulls_first(self) -> "Column":
"""Returns a Column expression with values sorted in descending order
(null values sorted before non-null values)."""
return Column(SortOrder(self._expression, Descending(), NullsFirst()))
def desc_nulls_last(self) -> "Column":
"""Returns a Column expression with values sorted in descending order
(null values sorted after non-null values)."""
return Column(SortOrder(self._expression, Descending(), NullsLast()))
def asc(self) -> "Column":
"""Returns a Column expression with values sorted in ascending order."""
return Column(SortOrder(self._expression, Ascending()))
def asc_nulls_first(self) -> "Column":
"""Returns a Column expression with values sorted in ascending order
(null values sorted before non-null values)."""
return Column(SortOrder(self._expression, Ascending(), NullsFirst()))
def asc_nulls_last(self) -> "Column":
"""Returns a Column expression with values sorted in ascending order
(null values sorted after non-null values)."""
return Column(SortOrder(self._expression, Ascending(), NullsLast()))
def like(self, pattern: ColumnOrLiteralStr) -> "Column":
"""Allows case-sensitive matching of strings based on comparison with a pattern.
Args:
pattern: A :class:`Column` or a ``str`` that indicates the pattern.
A ``str`` will be interpreted as a literal value instead of a column name.
For details, see the Snowflake documentation on
`LIKE <https://docs.snowflake.com/en/sql-reference/functions/like.html#usage-notes>`_.
"""
return Column(
Like(
self._expression,
Column._to_expr(pattern),
)
)
def regexp(self, pattern: ColumnOrLiteralStr) -> "Column":
"""Returns true if this Column matches the specified regular expression.
Args:
pattern: A :class:`Column` or a ``str`` that indicates the pattern.
A ``str`` will be interpreted as a literal value instead of a column name.
For details, see the Snowflake documentation on
`regular expressions <https://docs.snowflake.com/en/sql-reference/functions-regexp.html#label-regexp-general-usage-notes>`_.
:meth:`rlike` is an alias of :meth:`regexp`.
"""
return Column(
RegExp(
self._expression,
Column._to_expr(pattern),
)
)
def startswith(self, other: ColumnOrLiteralStr) -> "Column":
"""Returns true if this Column starts with another string.
Args:
other: A :class:`Column` or a ``str`` that is used to check if this column starts with it.
A ``str`` will be interpreted as a literal value instead of a column name.
"""
other = snowflake.snowpark.functions.lit(other)
return snowflake.snowpark.functions.startswith(self, other)
def endswith(self, other: ColumnOrLiteralStr) -> "Column":
"""Returns true if this Column ends with another string.
Args:
other: A :class:`Column` or a ``str`` that is used to check if this column ends with it.
A ``str`` will be interpreted as a literal value instead of a column name.
"""
other = snowflake.snowpark.functions.lit(other)
return snowflake.snowpark.functions.endswith(self, other)
def substr(
self,
start_pos: Union["Column", int],
length: Union["Column", int],
) -> "Column":
"""Returns a substring of this string column.
Args:
start_pos: The starting position of the substring. Please note that the first character has position 1 instead of 0 in Snowflake database.
length: The length of the substring.
:meth:`substring` is an alias of :meth:`substr`.
"""
return snowflake.snowpark.functions.substring(self, start_pos, length)
def collate(self, collation_spec: str) -> "Column":
"""Returns a copy of the original :class:`Column` with the specified ``collation_spec``
property, rather than the original collation specification property.
For details, see the Snowflake documentation on
`collation specifications <https://docs.snowflake.com/en/sql-reference/collation.html#label-collation-specification>`_.
"""
return Column(Collate(self._expression, collation_spec))
def get_name(self) -> Optional[str]:
"""Returns the column name (if the column has a name)."""
return (
self._expression.name
if isinstance(self._expression, NamedExpression)
else None
)
def __str__(self):
return f"Column[{self._expression}]"
def __repr__(self):
return f"Column({self._expression})" # pragma: no cover
def as_(self, alias: str) -> "Column":
"""Returns a new renamed Column. Alias of :func:`name`."""
return self.name(alias)
def alias(self, alias: str) -> "Column":
"""Returns a new renamed Column. Alias of :func:`name`."""
return self.name(alias)
def name(self, alias: str) -> "Column":
"""Returns a new renamed Column."""
return Column(Alias(self._expression, quote_name(alias)))
def over(self, window: Optional[WindowSpec] = None) -> "Column":
"""
Returns a window frame, based on the specified :class:`~snowflake.snowpark.window.WindowSpec`.
"""
if not window:
window = Window._spec()
return window._with_aggregate(self._expression)
def within_group(
self, *cols: Union[ColumnOrName, Iterable[ColumnOrName]]
) -> "Column":
"""
Returns a Column expression that adds a WITHIN GROUP clause
to sort the rows by the specified columns.
This method is supported on Column expressions returned by some
of the aggregate functions, including :func:`functions.array_agg`,
:func:`functions.listagg`, PERCENTILE_CONT(), and PERCENTILE_DISC().
For details, see the Snowflake documentation for the aggregate function
that you are using (e.g. `ARRAY_AGG <https://docs.snowflake.com/en/sql-reference/functions/array_agg.html>`_).
Examples::
>>> from snowflake.snowpark.functions import array_agg, col
>>> from snowflake.snowpark import Window
>>> df = session.create_dataframe([(3, "v1"), (1, "v3"), (2, "v2")], schema=["a", "b"])
>>> # create a DataFrame containing the values in "a" sorted by "b"
>>> df.select(array_agg("a").within_group("b").alias("new_column")).show()
----------------
|"NEW_COLUMN" |
----------------
|[ |
| 3, |
| 2, |
| 1 |
|] |
----------------
<BLANKLINE>
>>> # create a DataFrame containing the values in "a" grouped by "b"
>>> # and sorted by "a" in descending order.
>>> df_array_agg_window = df.select(array_agg("a").within_group(col("a").desc()).over(Window.partitionBy(col("b"))).alias("new_column"))
>>> df_array_agg_window.show()
----------------
|"NEW_COLUMN" |
----------------
|[ |
| 3 |
|] |
|[ |
| 1 |
|] |
|[ |
| 2 |
|] |
----------------
<BLANKLINE>
"""
return Column(
WithinGroup(
self._expression,
[
_to_col_if_str(col, "within_group")._expression
for col in parse_positional_args_to_list(*cols)
],
)
)
def _named(self) -> NamedExpression:
if isinstance(self._expression, NamedExpression):
return self._expression
else:
return UnresolvedAlias(self._expression)
@classmethod
def _to_expr(cls, expr: Union[ColumnOrLiteral, Expression]) -> Expression:
"""
Convert a Column object, or an literal value to an expression.
If it's a Column, get its expression.
If it's already an expression, return it directly.
If it's a literal value (here we treat str as literal value instead of column name),
create a Literal expression.
"""
if isinstance(expr, cls):
return expr._expression
elif isinstance(expr, Expression):
return expr
else:
return Literal(expr)
@classmethod
def _expr(cls, e: str) -> "Column":
return cls(UnresolvedAttribute(e, is_sql_text=True))
# Add these alias for user code migration
isin = in_
astype = cast
rlike = regexp
substring = substr
bitwiseAnd = bitand
bitwiseOR = bitor
bitwiseXOR = bitxor
isNotNull = is_not_null
isNull = is_null
eqNullSafe = equal_null
getName = get_name
getItem = __getitem__
class CaseExpr(Column):
"""
Represents a `CASE <https://docs.snowflake.com/en/sql-reference/functions/case.html>`_
expression.
To construct this object for a CASE expression, call the :func:`functions.when`
specifying a condition and the corresponding result for that condition.
Then, call :func:`when` and :func:`otherwise` methods to specify additional conditions
and results.
Examples::
>>> from snowflake.snowpark.functions import when, col, lit
>>> df = session.create_dataframe([[None], [1], [2]], schema=["a"])
>>> df.select(when(col("a").is_null(), lit(1)) \\
... .when(col("a") == 1, lit(2)) \\
... .otherwise(lit(3)).alias("case_when_column")).collect()
[Row(CASE_WHEN_COLUMN=1), Row(CASE_WHEN_COLUMN=2), Row(CASE_WHEN_COLUMN=3)]
"""
def __init__(self, expr: CaseWhen) -> None:
super().__init__(expr)
self._branches = expr.branches
def when(self, condition: ColumnOrSqlExpr, value: ColumnOrLiteral) -> "CaseExpr":
"""
Appends one more WHEN condition to the CASE expression.
Args:
condition: A :class:`Column` expression or SQL text representing the specified condition.
value: A :class:`Column` expression or a literal value, which will be returned
if ``condition`` is true.
"""
return CaseExpr(
CaseWhen(
[
*self._branches,
(
_to_col_if_sql_expr(condition, "when")._expression,
Column._to_expr(value),
),
]
)
)
def otherwise(self, value: ColumnOrLiteral) -> "CaseExpr":
"""Sets the default result for this CASE expression.
:meth:`else_` is an alias of :meth:`otherwise`.
"""
return CaseExpr(CaseWhen(self._branches, Column._to_expr(value)))
# This alias is to sync with snowpark scala
else_ = otherwise