Calculation within Pandas dataframe group

问题

I've Pandas Dataframe as shown below. What I'm trying to do is, partition (or groupby) by BlockID, LineID, WordID, and then within each group use current WordStartX - previous (WordStartX + WordWidth) to derive another column, e.g., WordDistance to indicate the distance between this word and previous word.

This post Row operations within a group of a pandas dataframe is very helpful but in my case multiple columns involved (WordStartX and WordWidth).

 *BlockID  LineID  WordID  WordStartX  WordWidth     WordDistance
0        0       0       0         275        150                 0
1        0       0       1         431         96   431-(275+150)=6        
2        0       0       2         642         90   642-(431+96)=115
3        0       0       3         746        104   746-(642+90)=14
4        1       0       0         273         69         ...
5        1       0       1         352        151         ...
6        1       0       2         510         92
7        1       0       3         647         90
8        1       0       4         752        105**

回答1:

The diff() and shift() functions are usually helpful for calculation referring to previous or next rows:

df['WordDistance'] = (df.groupby(['BlockID', 'LineID'])
        .apply(lambda g: g['WordStartX'].diff() - g['WordWidth'].shift()).fillna(0).values)

来源：https://stackoverflow.com/questions/40493829/calculation-within-pandas-dataframe-group