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pythonpandaslambda
Pete
Pete

Reputation: 449

How to calculate values row wise using lambda function?

So I have a dataframe where I want to count all the days a student was present. The dataframe headers are the days of the month and I want to count the frequency of the character 'P' row wise over all the columns and store them in a new column. What I have done unti now is defined a function which should accept each row and count the frequency of P -

def count_P(list):
    frequency = 0
    for item in list:
        if item == 'P':
            frequency += 1
    return frequency

And then I am trying to apply this function which is what I am confused about:

df['Attendance'] = df.apply(lambda x: count_P(x) for x in , axis = 1)

In the above line I need to pass x everytime as a row of the dataframe so do I write
for x in range(df.iloc[0],df.iloc[df.shape[0]])? But that gives me SyntaxError. And do I need axis here? Or does it need to be done in some other way?

Edit: The error message I am getting-

df['Attendance'] = df.apply(lambda x: count_P(x) for x in range(df.iloc[0],df.iloc[df.shape[0]]),axis=1)
                                ^
SyntaxError: Generator expression must be parenthesized

Upvotes: 0

Views: 687

Answers (1)

Christian Sloper
Christian Sloper

Reputation: 7510

Assuming your dataframe looks like this:

df = pd.DataFrame({'2021-03-01': ['P','P'], '2021-03-02': ['P','X']})

You can do :

df["p_count"] = (df == 'P').sum(axis=1)

yields:

    2021-03-01  2021-03-02  p_count
0   P           P           2
1   P           X           1

Upvotes: 4

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