dask.dataframe.DataFrame.eval

dask.dataframe.DataFrame.eval

DataFrame.eval(expr, inplace=None, **kwargs)[source]

Evaluate a string describing operations on DataFrame columns.

This docstring was copied from pandas.core.frame.DataFrame.eval.

Some inconsistencies with the Dask version may exist.

Operates on columns only, not specific rows or elements. This allows eval to run arbitrary code, which can make you vulnerable to code injection if you pass user input to this function.

Parameters
exprstr

The expression string to evaluate.

inplacebool, default False

If the expression contains an assignment, whether to perform the operation inplace and mutate the existing DataFrame. Otherwise, a new DataFrame is returned.

**kwargs

See the documentation for eval() for complete details on the keyword arguments accepted by query().

Returns
ndarray, scalar, pandas object, or None

The result of the evaluation or None if inplace=True.

See also

DataFrame.query

Evaluates a boolean expression to query the columns of a frame.

DataFrame.assign

Can evaluate an expression or function to create new values for a column.

eval

Evaluate a Python expression as a string using various backends.

Notes

For more details see the API documentation for eval(). For detailed examples see enhancing performance with eval.

Examples

>>> df = pd.DataFrame({'A': range(1, 6), 'B': range(10, 0, -2)})  
>>> df  
   A   B
0  1  10
1  2   8
2  3   6
3  4   4
4  5   2
>>> df.eval('A + B')  
0    11
1    10
2     9
3     8
4     7
dtype: int64

Assignment is allowed though by default the original DataFrame is not modified.

>>> df.eval('C = A + B')  
   A   B   C
0  1  10  11
1  2   8  10
2  3   6   9
3  4   4   8
4  5   2   7
>>> df  
   A   B
0  1  10
1  2   8
2  3   6
3  4   4
4  5   2

Multiple columns can be assigned to using multi-line expressions:

>>> df.eval(  
...     '''
... C = A + B
... D = A - B
... '''
... )
   A   B   C  D
0  1  10  11 -9
1  2   8  10 -6
2  3   6   9 -3
3  4   4   8  0
4  5   2   7  3

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