def projection(self, exprs):
"""
Compute new table expression with the indicated column expressions from
this table.
Parameters
----------
exprs : column expression, or string, or list of column expressions and
strings. If strings passed, must be columns in the table already
Returns
-------
projection : TableExpr
"""
import ibis.expr.analysis as L
if isinstance(exprs, (Expr, ) + six.string_types):
exprs = [exprs]
exprs = [self._ensure_expr(e) for e in exprs]
op = L.Projector(self, exprs).get_result()
return TableExpr(op)
def select(
self,
exprs: ir.ValueExpr | str | Sequence[ir.ValueExpr | str],
) -> TableExpr:
"""Compute a new table expression using `exprs`.
Passing an aggregate function to this method will broadcast the
aggregate's value over the number of rows in the table and
automatically constructs a window function expression. See the examples
section for more details.
Parameters
----------
exprs
Column expression, string, or list of column expressions and
strings.
Returns
-------
TableExpr
Table expression
Examples
--------
Simple projection
>>> import ibis
>>> fields = [('a', 'int64'), ('b', 'double')]
>>> t = ibis.table(fields, name='t')
>>> proj = t.projection([t.a, (t.b + 1).name('b_plus_1')])
>>> proj
r0 := UnboundTable[t]
a int64
b float64
Selection[r0]
selections:
a: r0.a
b_plus_1: r0.b + 1
>>> proj2 = t[t.a, (t.b + 1).name('b_plus_1')]
>>> proj.equals(proj2)
True
Aggregate projection
>>> agg_proj = t[t.a.sum().name('sum_a'), t.b.mean().name('mean_b')]
>>> agg_proj
r0 := UnboundTable[t]
a int64
b float64
Selection[r0]
selections:
sum_a: WindowOp(Sum(r0.a), window=Window(how='rows'))
mean_b: WindowOp(Mean(r0.b), window=Window(how='rows'))
Note the `Window` objects here.
Their existence means that the result of the aggregation will be
broadcast across the number of rows in the input column.
The purpose of this expression rewrite is to make it easy to write
column/scalar-aggregate operations like
>>> t[(t.a - t.a.mean()).name('demeaned_a')]
r0 := UnboundTable[t]
a int64
b float64
Selection[r0]
selections:
demeaned_a: r0.a - WindowOp(Mean(r0.a), window=Window(how='rows'))
"""
import ibis.expr.analysis as an
if isinstance(exprs, (Expr, str)):
exprs = [exprs]
projector = an.Projector(self, exprs)
op = projector.get_result()
return op.to_expr()
