SAS date function

[sameer112217]

No    Type                   ID        Month                  Amount

2411 Marine Cargo    1001    01APR2015         100
2411 Marine Cargo    1001    01MAY2015         200
2411 Marine Cargo    1001    01JUN2015         300
2411 Marine Cargo    1001    01AUG2015        100
2411 Marine Cargo    1001    01OCT2015        
2411 Marine Cargo    1001    01NOV2015         150

2411 Marine Cargo    1001    01DEC2015         50
2411 Marine Cargo    1001    01JAN2016         100
2411 Marine Cargo    1001    01FEB2016          200
2411 Marine Cargo    1001    01MAR2016
2411 Marine Cargo    1001    01APR2016         300
2411 Marine Cargo    1001    01MAY2016        500

2411 Marine Cargo    1001    01JUN2016        20
2411 Marine Cargo    1001    01SEP2016
2411 Marine Cargo    1001    01OCT2016       300
2411 Marine Cargo    1001    01DEC2016

I need the last year month value against the current one. Few sequence in the months column is missing like 01JUL2015, 01SEP2015 in the year 2015 and 01JUL2016, 01JUL2016 and 01NOV2016 , 01JAN2017, 01FEB2017, 01MAR2017 in the year 2016. I need Current year month-last year month ex (01Apr2016-01Apr2015)

I need the below results

No    Type                   ID        Month                  Amount       LY_Amount

2411 Marine Cargo    1001    01APR2015         100

2411 Marine Cargo    1001    01MAY2015

2411 Marine Cargo    1001    01JUN2015         200
2411 Marine Cargo    1001    01JUL2015         

2411 Marine Cargo    1001    01AUG2015        100

2411 Marine Cargo    1001    01SEP2015
2411 Marine Cargo    1001    01OCT2015        
2411 Marine Cargo    1001    01NOV2015        150

2411 Marine Cargo    1001    01DEC2015         50
2411 Marine Cargo    1001    01JAN2016         100
2411 Marine Cargo    1001    01FEB2016         200
2411 Marine Cargo    1001    01MAR2016
2411 Marine Cargo    1001    01APR2016        300         100
2411 Marine Cargo    1001    01MAY2016        500

2411 Marine Cargo    1001    01JUN2016         20           200

2411 Marine Cargo    1001    01JUL2016                         200

2411 Marine Cargo    1001    01AUG2016                       100

2411 Marine Cargo    1001    01SEP2016

2411 Marine Cargo    1001    01OCT2016

2411 Marine Cargo    1001    01NOV2016                       150

2411 Marine Cargo    1001    01DEC2016                         50

2411 Marine Cargo    1001    01JAN2017                       100
2411 Marine Cargo    1001    01FEB2017                       200

2411 Marine Cargo    1001    01MAR2017

This is just one set of group variables (2411 Marine Cargo   1001) from so many in my entire data.  I need the missing months in the column month for that particular and also the group variable values which is 2411, Marine Cargo, 1001 for the same.

I can then try lag function, lag12 for the same or intnx function or some sort of join. 

[andreas_lds]

I understood that you want to add observations for expected but missing month, but what rules are modifying Amount?

[sameer112217]

The amount should be zero for missing months. It should have blank values. and the character or group values should be same like below

2411  Marine Cargo    1001  

[andreas_lds]

Fine. And now please explain why you have

No   Type            ID      Month             Amount
2411 Marine Cargo    1001    01MAY2015         200

in the first table, and no value for Amount in the same observation in the second table.

No   Type            ID      Month             Amount
2411 Marine Cargo    1001    01MAY2015

[sameer112217]

Please ignore thats typo error. In short I need month comparison from last year based on the same granular grouping.