Clean up NULL values and copy good values on another Array CDT - a!forach loop with append() & inssert()

Question

Hi Community, 
 I am struggling with a simple expression rule. 
 I tried with append, insert and other functions, but i didn't manager. I expect those functions to return the previous array + the new addition. 
 I would like to generate a second array without "null" values of my CDT type, so I have an array only with proper data. 
 For that I did below expression rule: 
 
 load(
 local!itemsWithNull:{{null, null, 'type!{urn:com:appian:types}MyData'('uId': 5, 'name': "changed", 'symbol': "changed", 'market': "aa", 'isActive': false), null, null, null, null, 'type!{urn:com:appian:types}MyData'('name': "new", 'symbol': "new")}},
 local!itemsClean:{'type!{urn:com:appian:types}MyData'()},

 
 {a!forEach(
 items: (local!itemsWithNull),
 expression: {
 if(
 isnull(fv!item),
 fv!index & " is null",
 {
 "ADDED" & append(local!itemsClean,fv!item) & "END ADDED",
 }

 ) 
 }
 
 ),
 reverse(local!itemsClean),
 }

)

On my first iteration, I expect to get something like this (currently the expression rule is kind of in my debug mode :) ) 
 
 FIRST ITERATION 
 
 "ADDED[uId=5, name=changed, symbol=changed, market=aa, isActive=false]END ADDED" 
 However, I have something like this: 
 
 "ADDED[ uId=, name=, symbol=, market=, isActive=]; [uId=5, name=changed, symbol=changed, market=aa, isActive=false] END ADDED

SECOND ITERATION: 
 On my second iteration of valid data, I would expect to have a result like: 
 " [uId=5, name=changed, symbol=changed, market=aa, isActive=false]; [uId=, name= new , symbol=new, market=, isActive =] END ADDED" 
 However, I get something like this: 
 (the new data is present, but i lost my previous one) 
 "ADDED[uId=, name=, symbol=, market=, isActive=]; [uId=, name=new, symbol=new, market=, isActive=]END ADDED" 
 
 This is how my output looks like: 
 
 

List of Variant: 9 items
 List of Text String: 1 item
 "1 is null"
 List of Text String: 1 item
 "2 is null"
 List of Text String: 1 item
 "ADDED[uId=, name=, symbol=, market=, isActive=]; [uId=5, name=changed, symbol=changed, market=aa, isActive=false]END ADDED"
 List of Text String: 1 item
 "4 is null"
 List of Text String: 1 item
 "5 is null"
 List of Text String: 1 item
 "6 is null"
 List of Text String: 1 item
 "7 is null"
 List of Text String: 1 item
 "ADDED[uId=, name=, symbol=, market=, isActive=]; [uId=, name=new, symbol=new, market=, isActive=]END ADDED"
 MyData
 uId: null (Number (Integer))
 name: null (Text)
 symbol: null (Text)
 market: null (Text)
 isActive: null (Boolean) 
 
 Thanks very much in advance for any recommendation! 
 
 Best regards, 
 Manuel

erikm192 · Accepted Answer

Hi Manuel, 
 if you want to remove just null values from array what about using this expression? 
 
 load(
 local!itemsWithNull:{{null, null,'type!{urn:com:appian:types}MyData'('uId': 5, 'name': "changed", 'symbol': "changed", 'market': "aa", 'isActive': false), null, null, null, null, 'type!{urn:com:appian:types}MyData'('name': "new", 'symbol': "new")}},

 local!itemsClean: reject(fn!isnull,local!itemsWithNull),
 
 reverse(local!itemsClean)
)

erikm192 · Answer

Manuel, 
 1st problem: 
 Initialization of local!itemsClean. If you put there 'type!{urn:com:appian:types}MyData'() it means that there is already empty object. Thats why in first and second iteration of valid data you see first object empty. It is enough if you set it like local!itemsClean: {} 
 2nd problem 
 If you want to update other variables with some functions you have to do it from saveInto, so it means for example on button click. However if you want to filter array or do anything else you can do it directly on local variable. For your case like this: 
 local!itemsClean: a!forEach(
 items: local!itemsWithNull,
 expression: {
 if(
 isnull(fv!item),
 {},
 fv!item
 ) 
 }
 ) 
 
 What you see as output from your expression is output from forEach. Append, forEach and all appian functions (except a!save() ) are just returning text or other values, not doing any direct save. 
 
 Is it clearer now or do you have more questions? 
 Erik