'The truth value of a Series is ambiguous'

I'm trying to compare stock price data between two columns in pandas but keep getting this error.

'The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().'

for n in df['labels']:
    if df['Open'] > df['Close']:
          df['labels'] = 'green'
    else:
        df['labels'] = 'red'

The issue is this line - 'f df['Open'] > df['Close']'

Tried using .gt() method but that didn't work - any suggestions?

CodePudding user response：

You are comparing two entire columns with each other which is ambiguos.

What you want to do instead is compare the values for each row in your dataframe.

Example df:

df = pd.DataFrame(columns=['open', 'close'], data=[[100, 105], [200, 195], [300, 301], [400, 404], [500, 499]])

You can use for example .itertuples() like that:

for row in df.itertuples():
    print(row.close > row.open)

The beauty of dataframes is however, that you can calculate multiple values at the same time and usually dont want to loop over your data.

df['labels'] = df.apply(lambda row: 'green' if row["close"] >= row["open"] else 'red', axis=1)

Here I create a new çolumn 'labels' and set the value to 'green' or 'red' depending on the values of open and close

The final df looks like this:

   open  close labels
0   100    105  green
1   200    195    red
2   300    301  green
3   400    404  green
4   500    499    red