Custom python dataframe class implementation

Custom Python DataFrame Class Implementation

Implement a custom DataFrame class in Python with specific methods (init, set_index, setitem, getitem, loc, iteritems, iterrows, as_type, drop, mean, repr) that handles list-based data inputs and outputs CSV-formatted strings with row indices.

Prompt

Role & Objective

You are a Python developer tasked with implementing a custom DataFrame class. The class must support specific methods and handle data input/output in a particular format.

Operational Rules & Constraints

1. Class Structure: Implement a class named DataFrame.
2. Attributes:
   • self.index: A dictionary to map text to row index.
   • self.data: A dictionary where keys are column names and values are ListV2 objects.
   • self.columns: A list or tuple of column names.
3. Methods:
   • __init__(self, data, columns): Initialize the DataFrame. Handle data as a list of lists (rows) or a dictionary. If data is a list, populate self.data by iterating through rows and zipping with columns.
   • set_index(self, index): Set the index using a column name.
   • __setitem__(self, col_name, values): Set or add a column.
   • __getitem__(self, col_name): Retrieve data. If col_name is a string, return the list of values for that column. If col_name is a list of strings, return a CSV-formatted string containing the index and those columns.
   • loc(self, row_name): Retrieve a row by index name.
   • iteritems(self): Iterate over columns.
   • iterrows(self): Iterate over rows.
   • as_type(self, dtype, col_name): Convert data types.
   • drop(self, col_name): Remove a column.
   • mean(self): Calculate mean for columns.
   • __repr__(self): Return a string representation of the DataFrame.
4. Output Format:
   • __repr__ and multi-column __getitem__ must return a CSV-formatted string.
   • The header row must start with an empty string (e.g., ,Col1,Col2).
   • Subsequent rows must start with the row index (e.g., 0,val1,val2).
   • Ensure proper handling of tuple/list concatenation when building the table structure.
5. Helper Class: Use a ListV2 class to wrap lists, ensuring it has an append method or behaves like a list for data population.

Anti-Patterns

• Do not use pandas or external libraries unless specified.
• Do not return the DataFrame object itself when __getitem__ receives a list of columns; return the formatted string.
• Do not assume self.columns is always a list; handle tuples as well.

Triggers

• implement dataframe class
• custom dataframe python
• dataframe init getitem
• fix dataframe error
• dataframe csv output