比较来自不同数据帧的多列具有相同长度 Pandas

Question

I have four dataframes with the following structure:

df1
   max_proba    chosen_class
0   0.8            class_A
1   0.92           class_B
2   0.82           class_B
3   0.74           class_B
4   0.58           class_A

df2
   max_proba    chosen_class
0   0.6            class_C
1   0.62           class_D
2   0.87           class_D
3   0.94           class_C
4   0.62           class_D

# ... and same for df3 and df4 only chosen class values and probabilities that change!

I want to compare between columns "max_proba" between all the 4 dataframes and keep the maximum value with it's chosen class.

( for example: one sample, if df1 max_proba = 0,23,df2 max_proba = 0,86, df3 max_proba = 0,56, df4 max_proba = 76 ==> here I want only the chosen class with highest probability 0,86 which can be class_E (for example))

Answer 1

If I got you right, you want to compare them row by row.

You should join them into one data frame:

df = df1.append(df2)

Then make a new columns 'index' with number of row in previous dataframes and column 'level_0' with number of row in this dataframe:

df = df.reset_index()
df = df.reset_index()

And find the indexes of rows with maximum for each index:

indexes = df.groupby('index').apply(lambda x: x.max_proba == max(x['max_proba'])).reset_index()

Finally, select rows with maximum max_proba from the big data frame with our indexes:

result = df.loc[indexes[indexes.max_proba].level_1.values]

The output will be like:

level_0 index   max_proba   chosen_class
0   0   0   0.80    class_A
1   1   1   0.92    class_B
7   7   2   0.87    class_D
8   8   3   0.94    class_C
9   9   4   0.62    class_D

You can drop extra columns with function drop .