Pandas Looking At Next Row And Swapping Values

If i see a A&T consecutively, I will set found=True for A. set remove=True for T. Set value of T as A (copy A's value to T) Set T found=True If I see G&C consecutively,

Solution 1:

I would create some temporary columns to track the lagged flags and values and next flags. Then you can compare directly:

df['prior_flag'] = df.Flag.shift()
df['next_flag'] = df.Flag.shift(-1)
df['prior_value'] = df.Value.shift()

# Checkfor'A' followed by'T'
df.loc[(df.Flag =='A') & (df.next_flag =='T'), 'found'] =True
df.loc[(df.Flag =='T') & (df.prior_flag =='A'), 'remove'] =True
df.loc[(df.Flag =='T') & (df.prior_flag =='A'), 'Value'] = \
    df.loc[(df.Flag =='T') & (df.prior_flag =='A'), 'prior_value']

# Checkfor'G' followed by'C'
df.loc[(df.Flag =='G') & (df.next_flag =='C'), 'found'] =True
df.loc[(df.Flag =='C') & (df.prior_flag =='G'), 'remove'] =True
temp = df.loc[(df.Flag =='G') & (df.next_flag =='C'), 'Value'].values
df.loc[(df.Flag =='G') & (df.next_flag =='C'), 'Value'] = \
    df.loc[(df.Flag =='C') & (df.prior_flag =='G'), 'Value'].values
df.loc[(df.Flag =='C') & (df.prior_flag =='G'), 'Value'] = temp
df.drop(['next_flag', 'prior_flag', 'prior_value'], axis=1, inplace=True)

>>> df
  Flag Value  found remove
0    A     3TrueFalse1    T     3FalseTrue2    A     3FalseFalse3    A     4FalseFalse4    G     4TrueFalse5    C     3FalseTrue6    T     1FalseFalse

Because you want to swap values when G is followed by C, I created a temporary variable temp to store the intermediate copy value.

All temporary columns are then dropped at the end.

To view the remaining rows that have not been removed:

>>> df[~df.remove]
  Flag Value  found remove
0    A     3TrueFalse2    A     3FalseFalse3    A     4FalseFalse4    G     4TrueFalse6    T     1FalseFalse