python - pandas to_csv arguments float_format and decimal not working for index column -

background

i doing simulations resp. system analysis variing parameters (in case rpm only) , append every last line of results dataframe results_df summarizing dataframe df containing giving baviour of system in depencence of varied rpm.

in order appropriate index plotting , data analysis converted varied values (here rpm) list pandas series ser , concat series summarizing dataframe df containing results interested in.

since results of each calculation interested in last line of each calculation extracting data results dataframe results_df using .tail(1).

what have done far shown in following snippet:

rpm = [0.25, 0.3, 0.5, 0.75, 1.0, 1.5, 2.0]  ser = pd.series(rpm, name='rpm') df = pd.dataframe() df_list = list()  i, val in enumerate(rpm):     results_df = get_some_data_from_somwhere()     df_list.append(results_df.tail(1))  df = df.append(df_list, ignore_index=true) df = pd.concat([df, ser], axis=1) df.set_index('rpm', inplace=true)   open('foo.csv', 'w') f:     data.to_csv(f, index=true, header=true, decimal=',', sep=' ', float_format='%.3f') 

problem

this csv-file has follwing format:

rpm cooling_inner heating_inner cooling_outlet heating_outlet 0.25 303,317 323,372 302,384 324,332 

however, expected having 3 decimal digits , comma decimal sign on index column, shown here:

rpm cooling_inner heating_inner cooling_outlet heating_outlet 0,250 303,317 323,372 302,384 324,332 

so seems index , decimal sign options not applied index column when exporting dataframes csv-files using .to_csv command.

how achieve behaviour since index option set true , values (with exception index column) have right format , decimal sign?

do have handle index column somehow seperate?

i rewrite 2 bottom lines:

with open('foo.csv', 'w') f:     data.to_csv(f, index=true, header=true, decimal=',', sep=' ', float_format='%.3f') 

into

data.reset_index().to_csv('foo.csv', index=false, header=true, decimal=',', sep=' ', float_format='%.3f') 

this bit of workaround, have noticed, keyword arguments decimal= , float_format= work on data columns, not on index.

what instead put index dataframe reset_index , tell to_csv(index=false not save index file (since in data).

also, opening file stream (with open('foo.csv', 'w') f:) better left pandas, when give string 'foo.csv' first argument.