[go-nuts] Differences between maps and slices (performance)

It depends what the key is, how often it is modified and what the common
access patterns are.

Please provide the full context...
see https://code.google.com/p/go-wiki/wiki/HowToAsk ... it'll save time in
the discussion.

+ egon

The key never changes, it's something like this:

valid := map[string] int {
    "v=" : 0x1,
    "o=" : 0x2,
   // etc...
}

I need to do:

for _, line := range request {
   id, ok := valid[line[0:2]]
   if ok {
     // do something with id
   }
}

The other way to do it, is to do write something like so:

func in_string(a_char string, str []string) bool {
   for _, ch := range str {
     if ch == a_char {
       return true
     }
   }

   return false
}

...
valid_chars := []string{ "v", "o", }
if in_string(string(line[0:1]), valid_chars) && line[1:1] == "=" {
  ...
}


That's what I'm trying to do

How many valid key values are there?

Ian

in total - 16.

I still have no clue what those mean... nor whether the keys are unique, or
not, whether they have same prefixes or not. Please do not remove
information just because you think it's irrelevant, it makes the discussion
much longer and you may get poor suggestions as a result. Unless I'm able
to write the code that would solve your problem, then you are not giving
enough information. Read https://code.google.com/p/go-wiki/wiki/HowToAsk ,
especially the "The story of a bad question" part, there's a reason I
posted it.

All of those examples you provided are plausible, but given the context may
be suitable or not. There are of course more possibilities, like using
map[rune]map[rune]int or map[rune]int or []struct{a, b rune}, or a proper
trie... etc. Essentially profile for your needs.

You are not showing the full problem, which means you won't get a proper
answer.

+ egon

Sorry, but *NO*.
I asked a question, that I thought had enough information (access
information -> what is faster X or Y given when there are at least 1,000
access at given second).
It wasn't enough, so I gave an example on what I do (with actual data).
If that's not enough for you to help me, that's okay, but I do not know
what else to provide.
Others gave an answer that there are missing information, and explained
what is missing, but you just keep on pasting a document of "howto", that
does not explain a newbie like myself (not in programming, but in Go), and
very frustrating to deal with.

By giving me a FAQ, documents etc to read on how to ask, rather then to
explain to me what you are missing in my information, will not help me to
ask a better question, but rather not to ask at all.

I'll figure this out by myself, and might rewrite some code on my own, but
I can not provide more details, when I do not know what else is missing for
someone to help me understand, so thank you for your "help", but I guess
the mailing list is not the place for me.

Your question would have been much easier to answer if you had
provided a complete code sample. Since you say you only have 16
cases, that would have been easy to do.

With only 16 cases, I would go for the slice.

But really it's not going to matter. This is not going to be the hot
spot in your program

Ian

You still didn't give all the data and information what is the data... you
just gave a subset of a data.

I said I'm missing the *context*. I do not know what you are building. Is
it a game, is it a server, is it some data analysis front end, is it some
ACL etc. What are the other processes running on the server. What hardware
is the server running on. etc. What are you using to connect the clients.
Are you using WebSockets or do clients come with floppy disks to the server
and do a request?

Imagine I come to you and ask "What oil do I need to buy for my car, so it
would perform better?"... You ask me "What car is it and under what
conditions you are going to drive it in?"... and I reply "The car is blue
and it has 17 inch wheels."...

will not help me to ask a better question, but rather not to ask at all.
>

It's not a FAQ, it's a page explaining how much information you should give
and how to give it in the shortest way available. To me, it seemed you just
ignored that page... if the suggestion (i.e. reading the page) is unclear,
then say so and do not just skip commenting it; if you explain why it
wasn't clear, I can improve it or explain more...

I'll figure this out by myself, and might rewrite some code on my own, but
>

Here is the difficulty, I do not know what you are doing, hence I can not
ask you for the specifics without doing a 10 trip back-and-forth about the
system.

Either way will be fine for 1000 requests per second.

I don't understand whether you mean that there are 16 valid values, or
whether the data you are looking for has 16 elements. You also didn't
mention what the data type is. Can you show us a small program?

Ian

Yes and it's a benchmark performed at the machine the code will run
on. The results can be different between architectures, CPU steppings,
Go versions, etc.

-j

Benchmark it.
  http://dave.cheney.net/2013/06/30/how-to-write-benchmarks-in-go

Is there a better way? It doesn't sound like it, but I don't know if we
have enough details to know for sure.