Nested If () or Case. which is better

[Ted Giles]

The nested If() is about 8 layers deep, so is Case better?
Comments welcome.

[Keith Hubert]

Re: Nested If () or Case. which is better

Ted,

I would think that Case is better at that level, mainly because it is easier to control and you can even add to at a later time.

One other thought, you can include notation, if required.

[GGandhi]

Re: Nested If () or Case. which is better

hello
i am not an expert programmer but i like select case end select.
the code looks cleaner with one select end select and multiple case between the two, with one indentation.
and if you like to add if else end if in one or two case statements it is easy.
with if at 8 levels the indentation alone will ride off the screen and you need to keep track of end ifs to match the ifs. for me that is difficult.

performance wise they, probably, are similar, reading the code after sometime it is easy for me with select case end select.

[Stan Mathews]

Re: Nested If () or Case. which is better

Define better.

[Ted Giles]

Re: Nested If () or Case. which is better

Better = Faster and/or easier to code and understand later. Best use in a Calculated Field, or better in an Update Operation.

The dates or membership type in a record define the status of an account.
When payment is received, depending on the date, the status is as follows;

Payment made in Year to date = current.
Payment in previous year made in Sept, Oct, Nov, Dec = current
Payment in the 12 months prior to Sept in the previous year = lapsed
Membership type of A or B = current, irrespective of date paid.

I need to put the code into a calculated field rule or an update operation.

[GGandhi]

Re: Nested If () or Case. which is better

Faster?
If you know which will be the most frequent, then put them in top before other options then both select and if will perform equally fast. ( I think compilers compile select end select as if else if end if method secretively).

Easy to code and understand later?
For cleaner look and ease of reading, for me, still select end select is the way to go.

[Peter.Greulich]

Re: Nested If () or Case. which is better

Teed,

Conventional wisdom has it that IF is much faster than CASE. So if you are doing a loop w. thousands of records you might want to stick w. IF. OTOH, I generally use CASE for one time pass-thrus. I agree with the others that CASE is neater & cleaner and easier to read.

[TheSmitchell]

Re: Nested If () or Case. which is better

Teed,

Conventional wisdom has it that IF is much faster than CASE. So if you are doing a loop w. thousands of records you might want to stick w. IF. OTOH, I generally use CASE for one time pass-thrus. I agree with the others that CASE is neater & cleaner and easier to read.

Is there actually a difference? Has someone crunched the numbers?

[Ted Giles]

Re: Nested If () or Case. which is better

@Peter. I have about 6k records, so no big deal. Not like a county council with 30 million.LOL!

I am having a bit of a discussion with myself whether to do one complex pass of the table, or three more simple ones. The end result is the same, but on successive passes I can ignore field with data present so as my If () is now 14 deep, it might be quicker to pass through the table three times. We are talking about 15 seconds on my dev machine for all three. On a standard pc it would take 30 possibly, done 3 yimes a year.

My interest was more on the most professional approach.

@ Sarah. Not done it yet, but I can use the Stopwatch facility Al supplied and add it to the update. (See appropriate Timer Thread)
Will report back.

[csda1]

Re: Nested If () or Case. which is better

Hi Ted,

@Peter. I have about 6k records, so no big deal. Not like a county council with 30 million.LOL!

I am having a bit of a discussion with myself whether to do one complex pass of the table, or three more simple ones. The end result is the same, but on successive passes I can ignore field with data present so as my If () is now 14 deep, it might be quicker to pass through the table three times. We are talking about 15 seconds on my dev machine for all three. On a standard pc it would take 30 possibly, done 3 yimes a year.

My interest was more on the most professional approach.

@ Sarah. Not done it yet, but I can use the Stopwatch facility Al supplied and add it to the update. (See appropriate Timer Thread)
Will report back.

I have crunched the numbers in the past using my CSDA Code Utility timing function, and there is no measurable difference between the IF() and CASE() functions, nor IF-ELSE IF-ELSE-END IF and CASE SELECT-END SELECT code directives. For the latter pair, at the XBasic compiled level, they are different, but probably at the actual machine code level are probably close to identical.

As for single pass vs multi-pass through the tables, a more complicated expression (assuming you are not referencing external tables like in LookupC() and similar) only adds a little overhead, while each pass through the data adds a very large amount. ALWAYS DO LESS PASSES THROUGH THE DATA.

Also see my discussion on Alpha Five Speed with particular attention to the bullet on "evaluation of code". Assignments in Alpha Five have a high overhead versus expression evaluation.

[Mike Wilson]

Re: Nested If () or Case. which is better

Just to have it be said.... 14 if-then statements defines an algorithm of 16,384 variations. How on God's earth do you QC such a monster!?

[TheSmitchell]

Re: Nested If () or Case. which is better

I have crunched the numbers in the past using my CSDA Code Utility timing function, and there is no measurable difference between the IF() and CASE() functions, nor IF-ELSE IF-ELSE-END IF and CASE SELECT-END SELECT code directives. For the latter pair, at the XBasic compiled level, they are different, but probably at the actual machine code level are probably close to identical.

What do you mean by "xbasic compiled level"? xbasic is interpreted, if the deployment of WAS files is any indication.

[TheSmitchell]

Re: Nested If () or Case. which is better

Just to have it be said.... 14 if-then statements defines an algorithm of 16,384 variations. How on God's earth do you QC such a monster!?

Since the OP indicated that they could put their code in a SELECT-CASE, I have hunch that these 14 IF-THEN statements are nested 14 statements deep, which would mean there really are only 14 or 15 paths since nested statements would require previous statements to hold false in order to take the nested ELSE case. If that is the situation, they could alternatively leverage ELSEIF and eliminate the depth over utilizing the SELECT-CASE.

[Stan Mathews]

Re: Nested If () or Case. which is better

I see no mention by the OP of SELECT. I believe the thread should have been titled nested if() vs case() especially since he did mention use in a Calculated Field, or better in an Update Operation where select...case...end select would not be appropriate.

[Ted Giles]

Re: Nested If () or Case. which is better

Just to have it be said.... 14 if-then statements defines an algorithm of 16,384 variations. How on God's earth do you QC such a monster!?

I took the same view after a bit of experiment.
Went for several queries and ran them consecutively Mike.
Started with the easiest and then I could ignore the ones which had been processed.

Thanks for the info Ira, that is good to know. One less thing to worry about!