Pandas：创建数据帧而不按字母顺序自动排序列名

Question

I am creating an initial pandas dataframe to store results generated from other codes: eg

result = pd.DataFrame({'date': datelist, 'total': [0]*len(datelist), 
                       'TT': [0]*len(datelist)})

with datelist a predefined list. Then other codes will output some number for total and TT for each date , which I will store in the result dataframe.

So I want the first column to be date , second total and third TT . However, pandas will automatically reorder it alphabetically to TT , date , total at creation. While I can manually reorder this again afterwards, I wonder if there is an easier way to achieve this in one step.

I figured I can also do

result = pd.DataFrame(np.transpose([datelist, [0]*l, [0]*l]),
                      columns = ['date', 'total', 'TT'])

but it somehow also looks tedious. Any other suggestions?

Answer 1

You can pass the (correctly ordered) list of column as parameter to the constructor or use an OrderedDict:

# option 1:
result = pd.DataFrame({'date': datelist, 'total': [0]*len(datelist), 
                   'TT': [0]*len(datelist)}, columns=['date', 'total', 'TT'])

# option 2:
od = collections.OrderedDict()
od['date'] = datelist
od['total'] = [0]*len(datelist)
od['TT'] = [0]*len(datelist)
result = pd.DataFrame(od)

Answer 2

result = pd.DataFrame({'date': [23,24], 'total': 0,
                       'TT': 0},columns=['date','total','TT'])

Answer 3

Use pandas >= 0.23 in combination with Python >= 3.6.

result = pd.DataFrame({'date': datelist, 'total': [0]*len(datelist), 'TT': [0]*len(datelist)})

retains the dict's insertion order when creating a DataFrame (or Series) from a dict when using pandas v0.23.0 in combination with Python3.6.

See https://pandas.pydata.org/pandas-docs/version/0.23.0/whatsnew.html#whatsnew-0230-api-breaking-dict-insertion-order .