Python repeatable cycle for picking only first values equal 1-CodePudding

I have the df which has index with dates and values 0 or 1. I need to filter every first 1 from this data frame. For example:

2019-11-27    0
2019-11-29    0
2019-12-02    0
2019-12-03    1
2019-12-04    1
2019-12-05    1
2020-06-01    0
2020-06-02    0
2020-06-03    1
2020-06-04    1
2020-06-05    1

So I want to get:

2019-12-03    1
2020-06-03    1

CodePudding user response：

Assuming you want the first date with value 1 of the dataframe ordered by date ascending, a window operation might be the best way to do this:

df['PrevValue'] = df['value'].rolling(2).agg(lambda rowset: int(rowset.iloc[0]))

This line of code adds an extra column named "PrevValue" to the dataframe containing the value of the previous row or "NaN" for the first row.

Next, you could query the data as follows:

df_filtered = df.query("value == 1 & PrevValue == 0")

Resulting in the following output:

          date  value  PrevValue
3   2019-12-03      1        0.0
8   2020-06-03      1        0.0

CodePudding user response：

i built function that can satisfy your requirements

important note you should change the col argument it might cause you problem

  def funfun (df , col="values"):
  '''
  df : dataframe 
  col (str) : please insert the name of column that you want to scan 
  '''
  a = []
  c = df.to_dict()
  for i in range (len(c[col]) -1 ) : 
    b=c[col][i] , c[col][i 1]
    if b == (0, 1) : 
      a.append(df.iloc[i 1])
  return a

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