How to edit a measure to get the difference between two columns when one column value is blank?

[afleiderman1]

I got a quick question I got the following data

My rows are customer name

my column are weeks

my measure is sum of sales

and another measure from previous week sales 

                            Week 1                                                    Week 2                                                                          Week 3       

                       Previous    Week  diff           Previous        week                      diff                   PreviousWeek      Week          diff

James              blank           100          100                100            50                -50                       50                    60                  10

Fernando

Dresta

diff=thisweek-previous week

Since you see on the first week I have blank because I do not know what that value is because I have not brough it into the data set. Is there anyway to make my week difference value blank for the first week. 

[v-binbinyu-msft]

Hi @afleiderman1 ,

I'm a little confused about your needs, Could you please explain them further? It would be good to provide a screenshot of the results you are expecting and desensitized example data.

Thanks for your efforts & time in advance.

Best regards,
Community Support Team_Binbin Yu