update one field of CDT array

Question

Hi there, 
 I have one CDT array 
 { 
 {a: 1, 
 b: "R" 
 }, 
 {a: 2, 
 b: "E" 
 }, 
 {a: 3, 
 b: "R" 
 }, 
 } 
 what's the good way to update field b from "R" to "T". tried this, it does not work. 
 a!update(CDT.b, {1, 3}, "T") 
 anyone has the experience dong this? 
 Regards, 
 Lin

Dave Lewis · Answer

a!forEach(
 items: local!list,
 expression: if(
 fv!item.b = "R",
 update(
 data: fv!item,
 index: "b",
 value: "T"
 ),
 fv!item
 )
)

Mike Schmitt · Answer

Dave Lewis said: If you need null safety, index() function on line 4 
 fun fact: as far as i can tell, "fv!item" is null-safe for dot properties much like "fv!row" is - meaning, accessing a nonexistent property simply results in a null rather than an error. 
 a!localVariables(
 local!asdf: {
 {
 idx: 1
 },
 {
 idx: 2
 }
 },
 
 a!forEach(
 local!asdf,
 fv!item.name
 )
)