pandas how to count the number of rows whose column values add up to a threshold

Question

I have the following df,

pct    id

0.3    631

0.2    115

0.1    312

0.2    581

0.01   574

0.09   586

I want to first sort the df by pct,

df.sort_values(by=['pct'], ascending=False, inplace=True)

then adding up pct to 0.8 and count how many rows does that, e.g. top 4 rows in this case; I am wondering whats the best way to it. using pd.eval or pd.query?

Answer 1

Here is the python code to return the first records whose cumulative sum adds up a threshold:

threshold = 0.8

df1 = df [df ['pct'].cumsum().lt(threshold)]

print (df1)

output:

       pct   id

0    0.3   631

1    0.2   115

2   0.2   581

3   0.1   312

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