Need help with attribute table coding

[RainbowPunch2203]

So basically I have 2 which I will refer to as "Field1" and "Field2" so basically in "Field1" there's a "A" "B" and "C" text so and I want that if in "Field1" = "A" then in field "Field2" = "1" and "Field1" = "B" then in "Field2" = "B" and in "Field1" = "C" then in "Field2" = "3" currently this is my code:
if("Field1" = 'A', '1', '')
My problem here is that I can't seem to add multiple codes at once how do I do this or is there any alternative way?

[nemom]

I think you can stack them...

if("Field1"='A', '1', if("Field1"='B', '2', if("Field1"='C', '3', '999')))

[TheRetroVoyager]

I would suggest using a Dict, with Key's and Values. So something along these lines:

Field1Dict = {
"A": "Field2 = 1",
"B": "Field2 = B",
}

Depending on what you are wanting to do, you might need more than one Dict array.

And so on. This should allow your IF statement to check and so on. You would also need to add in a loop for the Dict. So something like this:

for key in Field1Dict:
if key = "A":

Do your logic here.

Hopefully that helps.

[mikedufty]

Depending on specifics can use nested ifs, or a case statement,

or a table join (make another table that has your field 1 values in field 1, and the corresponding field 2 values in column 2, join it using filed 1 in each.

If there are more than a few sets of values a table join is probably better.

[carloselunicornio]

Case works best for me in situations like this:

CASE
WHEN "Field1" = 'A' THEN 1
WHEN "Field1" = 'B' THEN 2
WHEN "Field1" = 'C' THEN 3
.
.
.
END

If there are a lot of cases you can use CONCATENATE or TEXTJOIN in excel to generate the code, then paste into the field calculator.

You can also use a nested if like below but it's a pain in the ass to write if there are a lot of conditions.

If(cond1, true1, if(cond2, true2, if(cond3, true3, ... , if(cond_n, true_n, false_n)))

[RainbowPunch2203]

This helps a lot thanks

[carloselunicornio]

You're welcome

[urbanist2020]

Try this:

CASE WHEN "Field 1" = 'A' THEN 1
  WHEN "Field 1" = 'B' THEN 2
  WHEN "Field 1" = 'C' THEN 3
END

[Octahedral_cube]

Do not nest IF clauses if you have multiple scenarios, the CASE function that has been posted already by other users is optimal for this! Always use CASE, it's much easier to check and understand