How can I give previous variable to current variable?-CodePudding

I have a list as below in python. In this list, the numbers are equal in some cases, but in cases where the numbers are equal, I want to print the value in the previous inequality in the 'c' column.

conditions  = [ df[a] > df[b], (df[a] == df[b]), df[a] < df[b] ]

choices     = [ "A bigger than B", 'same', 'B bigger than A' ]

df["c"] = np.select(conditions, choices, default=np.nan)

A	B	C
1	2	B bigger than A
2	2	same
2	2	same
3	2	A bigger than B
3	3	same
3	3	same
3	6	B bigger than A

i want to do

A	B	C
1	2	B bigger than A
2	2	B bigger than A
2	2	B bigger than A
3	2	A bigger than B
3	3	A bigger than B
3	3	A bigger than B
3	6	B bigger than A

CodePudding user response：

If values are equal, use previous as the comment. Otherwise, set comment conditionally.

previous = "same"
for i in range(len(df)):
  if df.loc[i,"A"] == df.loc[i,"B"]:
    comment = previous
  else:
    comment = "A bigger than B" if df.loc[i,"A"] > df.loc[i,"B"] else "B bigger than A"
  df.loc[i,"C"] = comment
  previous = comment

Result

  A  B                C
0  3  1  A bigger than B
1  1  2  B bigger than A
2  3  1  A bigger than B
3  1  1  A bigger than B
4  1  3  B bigger than A