Create python pandas series from dict, problem to assign index

问题

I am practicing my Python skills and want to create series. I want to use dictionary, but when I want to have index for the series, it shown to me NaN. I do not now what is the reason. The initial dictionary has string values for the keys and the values, contains only 8 elements.

country_capital_dict = {'Germany':'Berlin', 'US':'Washington',
                         'Italy':'Rome', 'France':'Paris',
                         'Russia':'Moscow','Spain':'Madrid',
                         'Austria':'Vienna','Greece':'Athens'}
country_capital_series = pd.Series(country_capital_dict, index = ['a','b','c','d','e','f','g','h'])
print(country_capital_series)

回答1:

If pass dictionary to Series from keys is created index by default:

country_capital_dict = {'Germany':'Berlin', 'US':'Washington',
                         'Italy':'Rome', 'France':'Paris',
                         'Russia':'Moscow','Spain':'Madrid',
                         'Austria':'Vienna','Greece':'Athens'}
country_capital_series = pd.Series(country_capital_dict)
print(country_capital_series)
Germany        Berlin
US         Washington
Italy            Rome
France          Paris
Russia         Moscow
Spain          Madrid
Austria        Vienna
Greece         Athens
dtype: object

If need change index you can assign it:

country_capital_series.index = ['a','b','c','d','e','f','g','h']

print(country_capital_series)
a        Berlin
b    Washington
c          Rome
d         Paris
e        Moscow
f        Madrid
g        Vienna
h        Athens
dtype: object

Or pass only values of dictionary to Series:

country_capital_series = pd.Series(country_capital_dict.values(), 
                                   index = ['a','b','c','d','e','f','g','h'])
print(country_capital_series)
a        Berlin
b    Washington
c          Rome
d         Paris
e        Moscow
f        Madrid
g        Vienna
h        Athens
dtype: object

Reason why get all missing values is mismatch between index from list and index from keys of dictionary - because different pandas try change original index by new from list and dont know new values, so assigned all NaNs:

country_capital_series = pd.Series(country_capital_dict, 
                                   index = ['a','b','c','d','e','f','g','h'])
print(country_capital_series)
a    NaN
b    NaN
c    NaN
d    NaN
e    NaN
f    NaN
g    NaN
h    NaN
dtype: object

If only some values matching are assigned NaNs only for not match values:

country_capital_series = pd.Series(country_capital_dict, 
                                   index = ['a','Germany','c','d','e','Austria','g','h'])
print(country_capital_series)
a             NaN
Germany    Berlin
c             NaN
d             NaN
e             NaN
Austria    Vienna
g             NaN
h             NaN
dtype: object

来源：https://stackoverflow.com/questions/65193488/create-python-pandas-series-from-dict-problem-to-assign-index

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python

pandas

series