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MR_105955561-Visitor
1-Visitor
June 21, 2024
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Match Function Error??

  • June 21, 2024
  • 4 replies
  • 3126 views

I'm trying to use the "match" function and having a very ridiculous problem. If there is no match, the function returns error. Works fine if there is a match. This makes it useless. As best I can tell from the documentation the return should be "-1" if there is no match. What obvious thing am I missing?

MR_10595556_0-1719004566233.png

 

Best answer by LucMeekes

Please point me to the location where it says that upon no match the function returns -1.

As far as I know, the reaction upon no match has always been an error.

LucMeekes_0-1719004985146.png

LucMeekes_1-1719004992332.png

Note that -1 is not a logic indication for no match, because you could set ORIGIN:=-1, which might mean that returning -1 the value was found at the first position. On the other hand, returning any (scalar) value should mean there's something wrong, because match is supposed to return a vector with the indices/positions (as you can see in the first example); but NaN could be another choice. However it was chosen to return an error in such cases.

If you want to get -1 upon no match, you'll have to write your own match() function, or embed it in a program where you trap the error:

LucMeekes_3-1719005570467.png

Success!

Luc

 

 

4 replies

L
LucMeekes23-Emerald IVAnswer
23-Emerald IV
June 21, 2024

Please point me to the location where it says that upon no match the function returns -1.

As far as I know, the reaction upon no match has always been an error.

LucMeekes_0-1719004985146.png

LucMeekes_1-1719004992332.png

Note that -1 is not a logic indication for no match, because you could set ORIGIN:=-1, which might mean that returning -1 the value was found at the first position. On the other hand, returning any (scalar) value should mean there's something wrong, because match is supposed to return a vector with the indices/positions (as you can see in the first example); but NaN could be another choice. However it was chosen to return an error in such cases.

If you want to get -1 upon no match, you'll have to write your own match() function, or embed it in a program where you trap the error:

LucMeekes_3-1719005570467.png

Success!

Luc

 

 

    W
    Werner_E25-Diamond I
    25-Diamond I
    June 21, 2024
    @MR_10595556 wrote:

    I'm trying to use the "match" function and having a very ridiculous problem. If there is no match, the function returns error.

    You may not like this behaviour and may think that different one would be more appropriate, but I won't call this  ridiculous.

     

     

    This makes it useless.

    I disagree, Would you also say the the implemented division operator is "useless" just because it throws an error when trying to divide b zero?

    Error trapping is up to the user.

     

     

    As best I can tell from the documentation the return should be "-1" if there is no match.

    No! This is not the case and never was. Maybe you confuse the "match" function for vectors and matrices with the "search"  function for strings!?

    -> String Functions

     

    As Luc already suggested you may redefine the match function to return something meaningful if no match is found. That way you may have more control to react accordingly.

    In Prime it may look like this:

    Werner_E_0-1719012356604.png

    Personally I would prefer a NaN as return value if no match was found.

     

    Note that the built-in "match" function has an optional third argument -> Lookup Functions

    When you type  "match" your (re)defined function is used and it will throw an error if third argument is used.

    Werner_E_1-1719012731530.png

     

    You still can use the built-in function if you label the word "match" as being "Function":

    Werner_E_2-1719012771731.png

    Note the different typeface.

     

    Of course you could also redefine the match function with the third argument:

    Werner_E_3-1719012852998.png

    So whenever you need the match function with its third argument, use the capital M, otherwise the lower case.

     

    You may hide the redefinition of the functions at the top of the sheet - either in a collapsed region or in the non-printable area to the right of the right margin.

     

    M
    MR_105955561-VisitorAuthor
    1-Visitor
    July 5, 2024

    Sorry if I offended. After reading the MathCAD help, documentation, searching the online community, and finally asking Chat GTP (that is where the -1 idea came from), I did not find any place that said the function returns "error" on no match. That might be obvious for people very close to it, but I suggest it needs to be stated explicitly because there are many platforms that have match functions and at least for me the idea that the result of no match is an error I have to write a handler for is outside of my experience. Just adding "the function returns "error" on no match" to the definition of the match function in the help file would have been an enormous help, especially since it is a different behavior than many people like me would expect from this function.

    W
    Werner_E25-Diamond I
    25-Diamond I
    July 6, 2024

    You did not offend and you sure a right that the documentation has (much) room for improvements.
    ChatGPT does not know much about Prime - after all Prime is not a mainstream software like MatLab or Maple.

    A
    anursinghCommunity Manager
    Community Moderator
    July 4, 2024

    Hi @MR_10595556,

     

    I wanted to follow up with you on your post to see if your question has been answered. 
    If so, please mark the appropriate reply as the Accepted Solution. 
    Of course, if you have more to share on your issue, please let the Community know so that we can continue to help you. 

     

    Thanks,
    Anurag

    S
    StuartBruff23-Emerald V
    23-Emerald V
    September 27, 2024
    @MR_10595556 wrote:

    I'm trying to use the "match" function and having a very ridiculous problem. If there is no match, the function returns error. Works fine if there is a match. This makes it useless. As best I can tell from the documentation the return should be "-1" if there is no match. What obvious thing am I missing?

    @LucMeekes wrote:

    Please point me to the location where it says that upon no match the function returns -1.

    As far as I know, the reaction upon no match has always been an error.

     

    Note that -1 is not a logic indication for no match, because you could set ORIGIN:=-1, which might mean that returning -1 the value was found at the first position. On the other hand, returning any (scalar) value should mean there's something wrong, because match is supposed to return a vector with the indices/positions (as you can see in the first example); but NaN could be another choice. However it was chosen to return an error in such cases.

    If you want to get -1 upon no match, you'll have to write your own match() function, or embed it in a program where you trap the error:

    LucMeekes_3-1719005570467.png

    Success!

    Luc

     

     

     

    Decisions, decisions.  I was going to post this replacement for match in another thread, but why not go the whole hog and reply to both - it might improve its visibility to others with the same problem.

     

    2024 09 27 G.png

     

    Where IsRange, vec, and search are defined as:

     

    2024 09 27 I.png

     

    I wouldn't go so far as to say built-in match's failure mode is useless, but I've always found it quite annoying.  If something doesn't seem intuitive and requires a workaround, then it probably needs fixing.  So I fixed it long ago, back in Original Mathcad 11 days of lore.

     

    The built-in match is part of the lookup suite of functions and is intended for searching arrays.  However, it seems a waste when it can be profitably used to search other data types, including strings.  So I gave it enhanced meaning and purpose along the way.

     

    Whilst the string data type has its search function to find a string within another string, search doesn't return the positions of all occurrences of the search string.  As I'd needed this capability on several occasions, I decided to simply overload match.

     

    In addition, if A is a range variable, new match expands it into a vector and then performs the search on that.

     

    Rather than -1 (or ORIGIN-1) to indicate a match failure, I opted for 0 (zero), 0 being the standard Mathcad boolean false.  I use 1 to indicate that a non-array (actual or implied) was the item being searched and that scalar/function z equals A (eg, 3 is 3 and cos is cos).  

     

    I've got a couple of versions of match kicking around in various stages of development.  A problem with the implementation shown above is that it uses the equality operator.  This is fine for a lot of data but can be problematic when dealing with reals.  Another version uses the built-in match with a standard lookup function modifier to deal with this scenario.  However, because user-defined functions can't take arbitrary numbers of arguments, I prefer to use the "standard" form where possible.  There are always tradeoffs and cat-skinning considerations to take into account.  

     

    Stuart

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