Python pandas automatically sorts columns

Question

i create a csv file from a pandas dataframe with lots of columns for our ERP system. Most of the columns are empty or constant, but the importtool of the system expects a csv file with a specified column order.

When creating the dataframe, i have something like that:

importlist = pd.DataFrame({ 'A': 'TestA',
                            'C': some values,
                            'B': '0'})

When i print the list, the columns are ordered A, B, C.

Is there a way to prevent automatical ordering? I know i could sort the columns manually again, but i think, this would't be a very nice solution, because there are about 50 columns.

Do you really create a dataframe like this or read data source from text file or database? — Parfait
– Parfait, Commented Jan 13, 2017 at 14:07
I have to create a DataFrame like this. This is a bill of material for pcbs which are imported in our ERP system. — Franz Forstmayr
– Franz Forstmayr, Commented Jan 13, 2017 at 18:23

Ted Petrou · Accepted Answer · 2017-01-13 14:17:24Z

3

For completeness, you can also use an OrderedDict which you pass a list of two element tuples where the first element of the tuple is the column name and the second element is a list of values.

pd.DataFrame(OrderedDict([('A',['TestA', 'TestB']), 
                          ('C', ['Some Item', 'Other Item']),
                         ('B',[0, 1])]))

       A           C  B
0  TestA   Some Item  0
1  TestB  Other Item  1

answered Jan 13, 2017 at 14:17

Ted Petrou

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Comments

jezrael · Accepted Answer · 2017-01-13 14:36:28Z

1

You need pass parameter columns with list of your columns of desired order, because default python dict is un-ondered:

importlist = pd.DataFrame({ 'A': 'TestA',
                        'C': some values,
                        'B': '0'}, columns = ['A','C','B'])

Sample:

importlist = pd.DataFrame({ 'A': ['TestA'],
                            'C':  [4],
                            'B': ['0']}, columns = ['A','C','B'])

print (importlist)
       A  C  B
0  TestA  4  0

Or use read_csv for reading csv if possible.

In docs are another methods for creating DataFrames, one of them is DataFrame.from_items:

a = ['TestA','TestB']
b = ['0', '7']
c = [4,7]

print (pd.DataFrame.from_items([('A', a), ('C', c),('B', b)]))
       A  C  B
0  TestA  4  0
1  TestB  7  7

edited Jan 13, 2017 at 14:36

answered Jan 13, 2017 at 14:04

jezrael

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