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How can I iteratively compare the current line with the previous and next lines in Pandas?

Is there any clever or Pythonic way to do something like the following in Pandas?

for index, row in pd.DataFrame().iterrows():
    if (row[previous_index]>=row and row[next_index]>=row):
       row=(row[previous_index]+row[next_index])/2
+3


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2 answers


Here's how you can implement it for Series using rolling_apply

. It is not clear how your comparisons will work on a whole row in the DataFrame.



In [5]: s = Series([1,2,3,2,5])

In [6]: def f(rows):
    if (rows[0] >= rows[1]) and (rows[2] >= rows[1]):
        return (rows[0] + rows[2]) / 2
    else:
        return rows[1]
   ...:     

In [7]: pd.rolling_apply(s, 3, f, center=True)
Out[7]: 
0   NaN
1     2
2     3
3     4
4   NaN
dtype: float64
+3


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I don't understand what operation you want to perform on strings, but the method shift

will work for you. (There are at Series.shift

and DataFrame.shift

.)



import pandas as pd
import numpy as np

np.random.seed(1)
ser = pd.Series(np.random.random_integers(0,10,10))

shift_down_by_one = ser.shift(1)
shift_up_by_one = ser.shift(-1)

mask = (shift_up_by_one >= ser) & (shift_down_by_one >= ser)
ser.loc[mask] = (shift_up_by_one + shift_down_by_one) / 2
+1


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