Summary  
This chapter covers how to read delimited text files into a pandas DataFrame using `pd.read_csv()` with the `sep`, `header`, and `names` parameters to control parsing, and how to extract individual rows via `.iloc[]`.  

General domain of usage  
Data analysis

Watch this video for a step-by-step explanation of how to read TXT files using pandas. You'll see how to use the `pd.read_csv()` function, set the correct `sep` parameter for text files, and handle files without column headers. This visual guide will reinforce the concepts from the chapter and help you confidently read and process TXT data in your own projects.

`pandas`で**テキストファイル**を読み込むには、同じ関数`pd.read_csv()`を使用可能。テキストファイルを正しく読み込むためには、**区切り文字**や**デリミタ**を指定する追加パラメータ`sep`の利用が重要。

```python
# Importing pandas library
import pandas as pd

# Reading a text file into a DataFrame
text_data = pd.read_csv('file.txt', sep='\r', header=None)
```

テキストファイルに**カラム名を含むヘッダー行**がない場合、`header`パラメータを`None`に設定。これにより、`pandas`は最初の行をカラム名として扱わない。

テキストファイルで一般的な改行を区切り文字として使用する場合、`sep='\r'`を設定。ここで、`'\r'`はキャリッジリターンを表し、新しい行を示す特殊文字。

注意

### 単一行の抽出

テキストファイルを`DataFrame`に読み込んだ後、`.iloc[]`を使い、取得したい行の位置を指定して個々の行にアクセス可能。

```python
# Extracting the first row
first_row = text_data.iloc[0]
```



`DataFrame` から単一の行（または単一の列）を選択すると、`pandas` は別の `DataFrame` ではなく、**`Series`** を返します。`Series` は一次元のラベル付き配列であり、インデックスとともに単一の値のシーケンスを保持しますが、別個の列構造は持ちません。このため、`first_row` は `text_data` とは少し異なる見た目や挙動になります。`.columns` は存在せず、表示すると各値の横にインデックスが表示され、表形式にはなりません。

import unittest
import importlib
import pandas as pd


# Helper function to dynamically generate test names and assertions
def _dynamic_test(test_case, condition, success_message, failure_message):
    if condition:
        test_case._testMethodName = success_message
        test_case.assertTrue(True, success_message)
    else:
        test_case._testMethodName = failure_message
        test_case.fail(failure_message)


def get_first_differing_row(expected_df, actual_df):
    expected_list = expected_df.astype(str).apply(tuple, axis=1)
    actual_list = actual_df.astype(str).apply(tuple, axis=1)

    for i, (row1, row2) in enumerate(zip(expected_list, actual_list)):
        if row1 != row2:
            return i, expected_df.iloc[i].values, actual_df.iloc[i].values

    if len(expected_df) > len(actual_df):
        return len(actual_df), expected_df.iloc[len(actual_df)].values, None
    else:
        return len(expected_df), None, actual_df.iloc[len(expected_df)].values


class TestUserCode(unittest.TestCase):

    def test_text_data_is_declared(self):
        import user_code
        _dynamic_test(
            self,
            hasattr(user_code, 'text_data'),
            "The `text_data` variable is declared.",
            "Expected `text_data` to be declared."
        )

    def test_text_data_is_dataframe(self):
        import user_code

        try:
            condition = isinstance(user_code.text_data, pd.DataFrame)
            failure_message = f"Expected `text_data` to be a `DataFrame`, but got `{type(user_code.text_data).__name__}`."
        except AttributeError:
            condition = False
            failure_message = "The `text_data` variable is not declared."

        _dynamic_test(
            self,
            condition,
            "The variable `text_data` is a `DataFrame`.",
            failure_message
        )

    def test_text_data_is_correct(self):
        import user_code
        row_1 = 'pandas is a software library written for the Python programming language for data manipulation and analysis. In particular, it offers data structures and operations for manipulating numerical tables and time series. It is free software released under the three-clause BSD license.[2] The name is derived from the term "panel data", an econometrics term for data sets that include observations over multiple time periods for the same individuals.[3] Its name is a play on the phrase "Python data analysis" itself.[4] Wes McKinney started building what would become pandas at AQR Capital while he was a researcher there from 2007 to 2010.[5]'
        row_2 = "taken from the site:"
        row_3 = "https://en.wikipedia.org/wiki/Pandas_(software)"
        expected_df = pd.DataFrame([row_1, row_2, row_3])

        variable = 'text_data'
        actual_df = getattr(user_code, variable, None)
        condition = False
        if actual_df is None:
            failure_message = f"The `{variable}` variable is not declared."
        elif not isinstance(actual_df, pd.DataFrame):
            failure_message = f"`{variable}` is not a `DataFrame`."
        elif actual_df.empty:
            failure_message = f"`{variable}` is empty."
        elif actual_df.equals(expected_df):
            condition = True
            failure_message = None
        else:
            idx, expected_row, actual_row = get_first_differing_row(expected_df, actual_df)
            failure_message = f"Expected `{variable}` to contain `{expected_row}` at row {idx}, but got `{actual_row}`."

        _dynamic_test(
            self,
            condition,
            f"`{variable}` contains the correct data.",
            failure_message
        )

    def test_first_row_is_declared(self):
        import user_code
        _dynamic_test(
            self,
            hasattr(user_code, 'first_row'),
            "The `first_row` variable is declared.",
            "Expected `first_row` to be declared."
        )

    def test_first_row_is_series(self):
        import user_code

        try:
            condition = isinstance(user_code.first_row, pd.Series)
            failure_message = f"Expected `first_row` to be a `Series`, but got `{type(user_code.first_row).__name__}`."
        except AttributeError:
            condition = False
            failure_message = "The `first_row` variable is not declared."

        _dynamic_test(
            self,
            condition,
            "The variable `first_row` is a `Series`.",
            failure_message
        )

    def test_first_row_is_correct(self):
        import user_code
        row_1 = 'pandas is a software library written for the Python programming language for data manipulation and analysis. In particular, it offers data structures and operations for manipulating numerical tables and time series. It is free software released under the three-clause BSD license.[2] The name is derived from the term "panel data", an econometrics term for data sets that include observations over multiple time periods for the same individuals.[3] Its name is a play on the phrase "Python data analysis" itself.[4] Wes McKinney started building what would become pandas at AQR Capital while he was a researcher there from 2007 to 2010.[5]'
        row_2 = "taken from the site:"
        row_3 = "https://en.wikipedia.org/wiki/Pandas_(software)"
        expected_df = pd.DataFrame([row_1, row_2, row_3])
        expected_value = expected_df.iloc[0]

        variable = 'first_row'
        actual_value = getattr(user_code, variable, None)
        if actual_value is None:
            condition = False
            failure_message = f"The `{variable}` variable is not declared."
        elif isinstance(actual_value, pd.Series):
            condition = actual_value.equals(expected_value)
            if actual_value.empty:
                failure_message = f"`{variable}` is empty."
            else:
                failure_message = f"Expected `{variable}` to contain `{expected_value.values}`, but got `{actual_value.values}`."
        else:
            condition = False
            failure_message = f"`{variable}` is not a `Series`."

        _dynamic_test(
            self,
            condition,
            f"`first_row` contains the correct values.",
            failure_message
        )


if __name__ == '__main__':
    unittest.main()

test_main.py

Pandasは、データ分析のための非常にユーザーフレンドリーなライブラリです。また、DataFrameやSeriesのようなデータ構造を使用して大規模なデータセットを扱うように設計されています。これにより、データサイエンスにとって不可欠なツールとなっています。本ガイドでは、相関、最頻値、中央値、最大値および最小値の算出方法など、さまざまな統計関数について学びます。また、欠損値の処理や特定の値の操作、削除方法についても習得します。

pandasライブラリの基本を学びます。SeriesおよびDataFrameの作成と操作、その構造の探索、基本的なデータ操作の実践に自信を持つことができます。

CSVファイルおよびTXTファイルからデータを読み込み、管理する方法を習得します。pandasツールを使用してデータセットをインポートし、さらなる分析のために準備する実践的な経験を得られます。

データを効果的に探索、クリーンアップ、要約する方法を学びます。欠損値の処理方法、インサイトの抽出、pandasを用いた基本的な統計操作について理解します。

TXTファイル

単一行の抽出

解答