maxframe.dataframe.DataFrame.mf.apply_chunk#

DataFrame.mf.apply_chunk(func: str | Callable, batch_rows=None, dtypes=None, dtype=None, name=None, output_type=None, index=None, skip_infer=False, args=(), **kwargs)#

Apply a function that takes pandas DataFrame and outputs pandas DataFrame/Series. The pandas DataFrame given to the function is a chunk of the input dataframe, consider as a batch rows.

The objects passed into this function are slices of the original DataFrame, containing at most batch_rows number of rows and all columns. It is equivalent to merging multiple df.apply with axis=1 inputs and then passing them into the function for execution, thereby improving performance in specific scenarios. The function output can be either a DataFrame or a Series. apply_chunk will ultimately merge the results into a new DataFrame or Series.

Don’t expect to receive all rows of the DataFrame in the function, as it depends on the implementation of MaxFrame and the internal running state of MaxCompute.

Parameters:

func (str or Callable) – Function to apply to the dataframe chunk.
batch_rows (int) – Specify expected number of rows in a batch, as well as the len of function input dataframe. When the remaining data is insufficient, it may be less than this number.
output_type ({'dataframe', 'series'}, default None) – Specify type of returned object. See Notes for more details.
dtypes (Series, default None) – Specify dtypes of returned DataFrames. See Notes for more details.
dtype (numpy.dtype, default None) – Specify dtype of returned Series. See Notes for more details.
name (str, default None) – Specify name of returned Series. See Notes for more details.
index (Index, default None) – Specify index of returned object. See Notes for more details.
skip_infer (bool, default False) – Whether infer dtypes when dtypes or output_type is not specified.
args (tuple) – Positional arguments to pass to func in addition to the array/series.
**kwds – Additional keyword arguments to pass as keywords arguments to func.

Returns:

Result of applying func along the given chunk of the DataFrame.

Return type:

Series or DataFrame

See also

DataFrame.apply: For non-batching operations.
Series.mf.apply_chunk: Apply function to Series chunk.

Notes

When deciding output dtypes and shape of the return value, MaxFrame will try applying func onto a mock DataFrame, and the apply call may fail. When this happens, you need to specify the type of apply call (DataFrame or Series) in output_type.

For DataFrame output, you need to specify a list or a pandas Series as dtypes of output DataFrame. index of output can also be specified.
For Series output, you need to specify dtype and name of output Series.
For any input with data type pandas.ArrowDtype(pyarrow.MapType), it will always be converted to a Python dict. And for any output with this data type, it must be returned as a Python dict as well.

Examples

>>> import numpy as np
>>> import maxframe.tensor as mt
>>> import maxframe.dataframe as md
>>> df = md.DataFrame([[4, 9]] * 3, columns=['A', 'B'])
>>> df.execute()
   A  B
0  4  9
1  4  9
2  4  9

Use different batch_rows will collect different dataframe chunk into the function.

For example, when you use batch_rows=3, it means that the function will wait until 3 rows are collected.

>>> df.mf.apply_chunk(np.sum, batch_rows=3).execute()
A    12
B    27
dtype: int64

While, if batch_rows=2, the data will be divided into at least two segments. Additionally, if your function alters the shape of the dataframe, it may result in different outputs.

>>> df.mf.apply_chunk(np.sum, batch_rows=2).execute()
A     8
B    18
A     4
B     9
dtype: int64

If the function requires some parameters, you can specify them using args or kwargs.

>>> def calc(df, x, y):
...    return df * x + y
>>> df.mf.apply_chunk(calc, args=(10,), y=20).execute()
    A    B
0  60  110
1  60  110
2  60  110

The batch rows will benefit the actions consume a dataframe, like sklearn predict. You can easily use sklearn in MaxFrame to perform offline inference, and apply_chunk makes this process more efficient. The @with_python_requirements provides the capability to automatically package and load dependencies.

Once you rely on some third-party dependencies, MaxFrame may not be able to correctly infer the return type. Therefore, using output_type with dtype or dtypes is necessary.

>>> from maxframe.udf import with_python_requirements
>>> data = {
...     'A': np.random.rand(10),
...     'B': np.random.rand(10)
... }
>>> pd_df = pd.DataFrame(data)
>>> X = pd_df[['A']]
>>> y = pd_df['B']

>>> from sklearn.model_selection import train_test_split
>>> from sklearn.linear_model import LinearRegression
>>> model = LinearRegression()
>>> model.fit(X, y)

>>> @with_python_requirements("scikit-learn")
... def predict(df):
...     predict_B = model.predict(df[["A"]])
...     return pd.Series(predict_B, index=df.A.index)

>>> df.mf.apply_chunk(predict, batch_rows=3, output_type="series", dtype="float", name="predict_B").execute()
0   -0.765025
1   -0.765025
2   -0.765025
Name: predict_B, dtype: float64

Create a dataframe with a dict type.

>>> import pyarrow as pa
>>> import pandas as pd
>>> from maxframe.lib.dtypes_extension import dict_
>>> col_a = pd.Series(
...     data=[[("k1", 1), ("k2", 2)], [("k1", 3)], None],
...     index=[1, 2, 3],
...     dtype=dict_(pa.string(), pa.int64()),
... )
>>> col_b = pd.Series(
...     data=["A", "B", "C"],
...     index=[1, 2, 3],
... )
>>> df = md.DataFrame({"A": col_a, "B": col_b})
>>> df.execute()
                        A  B
1  [('k1', 1), ('k2', 2)]  A
2             [('k1', 3)]  B
3                    <NA>  C

Define a function that updates the map type with a new key-value pair in a batch.

>>> def custom_set_item(df):
...     for name, value in df["A"].items():
...         if value is not None:
...             df["A"][name]["x"] = 100
...     return df

>>> mf.apply_chunk(
...     process,
...     output_type="dataframe",
...     dtypes=md_df.dtypes.copy(),
...     batch_rows=2,
...     skip_infer=True,
...     index=md_df.index,
... )
                                    A  B
1  [('k1', 1), ('k2', 2), ('x', 10))]  A
2              [('k1', 3), ('x', 10)]  B
3                                <NA>  C

maxframe.dataframe.DataFrame.mf.apply_chunk#

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