Vlookup to replace column index with value for each row in python dataframes

Question

I have a data frame of some registered velocities (V1, V2, V3, MaxV or the maximum velocity) and the corresponding time stamps for each velocity(T1, T2, T3, MaxV_T or the time instant of the maximum velocity) as follows:

df

Event T1       V1    T2       V2    T3       V3    MaxV  MaxV_T
  0   12:40:44 42.86 12:40:43 45.65 12:40:39 50.5  50.5  T3
  1   15:28:15 88.75 15:28:14 86.45 15:28:17 84.56 88.75 T1

The point that in the MaxV_T column doesn't indicate the real value but the title of the column where the real value falls.

What i need to do in python is to replace this value with the real time stamp to be like this

df

Event T1       V1    T2       V2    T3       V3    MaxV  MaxV_T
  0   12:40:44 42.86 12:40:43 45.65 12:40:39 50.5  50.5  12:40:39
  1   15:28:15 88.75 15:28:14 86.45 15:28:17 84.56 88.75 15:28:15

UPDATE

What to do if the position indication is not available, so i don't have the initial MaxV_T column and i need to return the corresponding time value for each velocity?

piRSquared · Accepted Answer · 2017-05-15 16:06:01Z

3

Use lookup

df.assign(MaxV_T=df.lookup(df.index, df.MaxV_T))

   Event        T1     V1        T2     V2        T3     V3   MaxV    MaxV_T
0      0  12:40:44  42.86  12:40:43  45.65  12:40:39  50.50  50.50  12:40:39
1      1  15:28:15  88.75  15:28:14  86.45  15:28:17  84.56  88.75  15:28:15

answered May 15, 2017 at 16:06

piRSquared

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2 Comments

Mshendy Over a year ago

I have an update for the question. What to do if the position indication is not available, so i don,t have the column MaxV_T and i need to return the corresponding time value for each velocity?

piRSquared Over a year ago

@Mshendy I'm confused about what you want. I'd suggest a new question where you can explain the "position not available " more clearly

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