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The length of the x-axis can be defined by removing some strings at the end of the list which is used for x-axis.  code:       

# Filter the DataFrame to include only rows where the 'Class' column matches 'AY' 

df_filtered = df[df.index.isin(['AY', 'A', 'B'])] 

# Set font to serif 

rcParams['font.family'] = 'serif' 

# Plotting 

plt.figure(figsize=(10, 6)) 

for col in df_filtered.columns: 

plt.plot(df_filtered.index, df_filtered[col], marker='o', label=col) 

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Plot with letters as x-axis . Code:
         
          
       Output:    
                    

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Set the limit of x-axis Code:
         
          
       Output:    
                    

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