Pandas check if two conditions are true and change row

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I have a pandas dataframe with four columns: ['Source', 'Target', 'Type', 'Weight']

The combination of 'Source' and 'Weight' is basically the key for the dataframe, so at most one combination of 'Source' and 'Weight' is possible.

Now I want to check, whether a certain row is already in the dataframe, if so, access it (by adding +1 to Weight) and if not, create it.

How can I search for two conditions, access if there is a match and create a new row if not?

    if(df[(df.Source == source) & (df.Target == target)].empty()):
        df = df.append([source, target, 'bidirectional', 1])
    else:
        df[(df.Source == source) & (df.Target == target)].Weight += 1
pandas dataframe python-3.x python
1 Answers

It would be rather following function:

def add(df, source, target):
  if df[(df.Source == source) & (df.Target == target)].empty:
    df.loc[max(df.index) + 1] = [source, target, 'bidirectional', 1]
  else:
    df.loc[(df.Source == source) & (df.Target == target), "Weight"] += 1
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