如何在for循环中生成Python lambda过滤代码？

Question

I am a beginner to Python lambda. And try to convert the Python for loop to lambda expression. First I would like to explain the for loop lines.

fred = Fred2Hdfs() # construct the python imported objects

for i, state in enumerate(us_states):
    df_unemployee_annual = fred.getFredDF('A', state, 'search_text')  # generate dataframe from the object
    if df_unemployee_annual is None:
        continue
    
    if i == 0:
        fred.writeCsv2Hdfs('unemployee_annual.csv', df_unemployee_annual)  # write dataframe 
    else:
        fred.appendCsv2Hdfs('unemployee_annual.csv', df_unemployee_annual)  # append dataframe

The above code work successfully without errors. And below codes are the Python lambda codes which I try to convert.

fred = Fred2Hdfs()

freq='A'
str='search_text'
result_df_list = list(map(lambda state: fred.getFredDF(freq, state, str), us_states))
result_df_list = list(filter(lambda df: df is not None, result_df_list))
print(result_df_list)  # codes work correctly until this line.
#func=map(lambda df:fred.writeCsv2Hdfs('unemployee_annual_.csv', df) , result_df_list)

I am stuck with if i==0: line in the for loop. How can I make the appropriate Python lambda expression from if i==0: line. I am afraid I have no idea how to implement the if filter of Python lambda.

Answer 1

map(lambda (i,df):fred.writeCsv2Hdfs('unemployee_annual_.csv', df) if i == 0 else fred.appendCsv2Hdfs('unemployee_annual_.csv', df) , enumerate(result_df_list))