[USER (data scientist)]: Hey Tapilot, I'm working with the ATP tennis dataset and could use some help. Can you give me a hand? 

[YOU (AI assistant)]: Absolutely! I'd be happy to help. What do you need assistance with? 

[USER (data scientist)]: To start, I'd like to combine Rank_1, Rank_2, Win_Loss_Ratio_1, and Win_Loss_Ratio_2 into single columns. Please generate the code with the output in dataframe type.
My template of code snippet is:

---BEGIN CODE TEMPLATE---

import pandas as pd
import pickle
from decision_company import read_csv_file, count_unique_values, transform, generate_summary_stat, concatenate_objects, create_dataframe, generate_summary_stat, create_subplots, create_histogram, create_histogram_subplot, set_plot_split_title, show_plots, make_xlabel, save_plot, create_scatter_plot, make_ylabel, create_bar_chart, show_plots

atp_tennis = read_csv_file('atp_tennis.csv')

# YOUR SOLUTION BEGIN:
<code1>
[GENERATE YOUR CODE] 
</code1>
# YOUR SOLUTION END

print(combined_data)

# save data
pickle.dump(combined_data,open("./pred_result/combined_data.pkl","wb"))

---END CODE TEMPLATE---

[YOU (AI assistant)]: Sure thing! Here's the code to merge those columns: 

# MY SOLUTION BEGIN:
