How to subset data and set values based on matching dates

[gbwit]

I have a table like:

id    date                   value       new

x      01/01/2019          1

y      01/01/2019          2

x      01/02/2019          1

z     01/03/2019           1

I am trying to select where id=x,y

Then, once I have that subset, I want to check if x has a corresponding y of the same date -  if it does, then I want to set new to value where y - for both x and y; otherwise, new is just set to value

so the table would become

id    date                   value       new

x      01/01/2019          1             2

y      01/01/2019          2             2

x      01/02/2019          1             1

z     01/03/2019           1             1

I am totally unsure how to go about this,

I began by subsetting my data:

IF id='x' OR id='y' THEN DO;

/*...*/

END;

ELSE new=value;

any help would be appreciated

Also, I cannot use the actual dates in my code

[Reeza]

I'm guessing that you also need to generalize this or is this the exact change you need? Why do x and y go together?

[gbwit]

I don't need to generalize the id, I know specifically that I need to be comparing/ checking x and y (y is a follow up for x in the data I am using)