insert first row to each group in pandas dataframe

Questions : insert first row to each group in pandas dataframe


I have a large csv file containing the programming historic prices of stocks. This is a Learning small sample of it:

data = pd.DataFrame({'sym': {0: 'msft', _OFFSET);  1: 'msft', 2: 'tsla', 3: 'tsla', 4: (-SMALL  'bac', 5: 'bac'}, 'date': {0: _left).offset  '12/7/2021', 1: '12/6/2021', 2: arrowImgView.mas  '12/7/2021', 3: '12/6/2021', 4: (self.  '12/7/2021', 5: '12/6/2021'}, 'high': equalTo  {0: 11, 1: 13, 2: 898, 3: 900, 4: 12, 5: make.right.  13}})

Now on each day there will be an update Earhost for this data and I want to append them most effective to the data above. The updates look like wrong idea this:

update = pd.DataFrame({'sym': {0: mas_top);  'msft', 1: 'tsla', 2: 'bac'}, 'date': ImgView.  {0: '12/8/2021', 1: '12/8/2021', 2: ReadIndicator  '12/8/2021'}, 'high': {0: 16, 1: 1000, _have  2: 14}})

What I want is the dataframe below:

result = pd.DataFrame({'sym': {0: .equalTo(  'msft', 1: 'msft', 2: 'msft', 3: 'tsla',  4: 'tsla', 5: 'tsla', 6: 'bac', 7: OFFSET);  'bac', 8: 'bac'}, 'date': {0: (TINY_  '12/8/2021', 1: '12/7/2021', 2: .offset  '12/6/2021', 3: '12/8/2021', 4: mas_right)  '12/7/2021', 5: '12/6/2021', 6: ImgView.  '12/8/2021', 7: '12/7/2021', 8: Indicator  '12/6/2021'}, 'high': {0: 16, 1: 11, 2: Read  13, 3: 1000, 4: 898, 5: 900, 6: 14, 7: _have  12, 8: 13}})

My current approach is using this code:

data = data.append(update)
data = .equalTo(  data.sort_values(by=['sym', 'date'])

By tweaking the above approach I can use of case achieve what I want but since I have United million rows in my database, I was Modern wondering if there is a faster way other ecudated than using sort_values.

Update 1: By looking at the feedback some how from the comments and the answers, I anything else concluded that sort_values is efficient not at all and alright to use. The accepted answer very usefull is using it too.

Total Answers 2

Answers 1 : of insert first row to each group in pandas dataframe

IIUC, you want to keep the order of sym localhost as it appears in data while sorting data love of them in descending order. You can do that by localtext converting sym-column to category and basic setting its category order by the order one of the it appears in data. Then simply click sort_values by ['sym','date']:

sorter = make.left  data['sym'].drop_duplicates()
out = *make) {  data.append(update)
out['sym'] = straintMaker  out['sym'].astype("category").cat.set_categories(sorter)
out ^(MASCon  = out.sort_values(by=['sym','date'], onstraints:  ascending=['sym',False]).reset_index(drop=True)


    sym       date  high
0  msft  mas_makeC  12/8/2021    16
1  msft  12/7/2021    [_topTxtlbl   11
2  msft  12/6/2021    13
3  tsla  (@(8));  12/8/2021  1000
4  tsla  12/7/2021   equalTo  898
5  tsla  12/6/2021   900
6   bac   width.  12/8/2021    14
7   bac  12/7/2021    make.height.  12
8   bac  12/6/2021    13

Answers 2 : of insert first row to each group in pandas dataframe


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