Solving Pandas TypeError: no numeric data to plot (4 solutions)

Updated: February 21, 2024 By: Guest Contributor Post a comment

The Problem

Encountering the TypeError: no numeric data to plot can be a common issue for those working with data visualization in Pandas. This error occurs when Pandas attempts to plot a graph but finds that the data provided does not contain numeric types that can be quantitatively represented on a plot. Below are some key reasons and strategic solutions to effectively address this issue.

Reasons for the Error

  • Data contains non-numeric types (e.g., strings or objects).
  • Numeric data are wrongly interpreted as objects or categories.
  • Attempting to plot empty or NaN values.

Solutions to Fix the Error

1. Convert Data to Numeric

This involves explicitly converting column data types to numeric using Pandas to_numeric() function. This is a straightforward approach when you have columns that are stored as strings or objects but contain numeric values in reality.

  1. Identify columns causing the issue.
  2. Use pandas.to_numeric() for conversion.
  3. Optionally, handle conversion errors with the errors parameter.

Code Example:

import pandas as pd
df = pd.DataFrame({'a': ['1', '2', '3'], 'b': ['4', '5', 'cat']})
df['a'] = pd.to_numeric(df['a'])
df['b'] = pd.to_numeric(df['b'], errors='coerce')

Notes: This method ensures that all values are numeric, with non-numeric values converted or set to NaN. However, it doesn’t rectify the root problem if the non-numeric data was unexpected. Always check why non-numeric data exists first.

2. Drop Non-Numeric Columns

Sometimes, it’s practical to remove non-numeric columns entirely if they are not relevant for the plotting. This can be done by selecting only the numeric columns before plotting.

  1. Identify and select numeric columns using select_dtypes().
  2. Plot the DataFrame after selection.

Code Example:

import pandas as pd
df = pd.DataFrame({...})  # Assuming df is your dataframe
numeric_df = df.select_dtypes(include=['number'])
# Now numeric_df can be plotted without issues

Notes: While effective, be aware that this method may neglect potentially important information contained in non-numeric columns that might be relevant for analysis, but not for direct plotting.

3. Handle Missing or NaN Values

Missing values or NaNs can also trigger this error if not properly handled. Ensuring that your DataFrame’s numeric columns are free of NaN values or deciding on a strategy to deal with them is essential.

  1. Identify columns with NaN values.
  2. Choose a method to handle these (e.g., fillna, dropna).
  3. Apply the chosen method.

Code Example:

import pandas as pd
df = pd.DataFrame({...})  # An example dataframe
# Replace NaN with 0 (or other relevant value)
df.fillna(0, inplace=True)
# Or, to drop rows with any NaN values

Notes: This approach directly addresses the plotting issue by ensuring data integrity, but may alter the dataset significantly depending on the chosen method to handle missing values.

4. Ensure Correct Plotting Method

Finally, double-check that the correct Pandas plotting function is being used for your data. For instance, categorical data might be better represented with a barplot instead of a line plot.

  1. Review the data and matching plot types.
  2. Select an appropriate Pandas plot type based on your data characteristics.

This solution depends heavily on matching the data type with the suitable plot. Thus, understanding Pandas plot types and their correct use cases is crucial.

Notes: This solution emphasizes the importance of appropriate plot selection which can significantly enhance the clarity and effectiveness of your data visualization.