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Doing math on text.

MorrisDH

Pardon the vague subject title but briefly describing the issue is not easy.

Starting with a string that contains a 'list' of numbers. The word 'list' is in quotes because it is not a SKILL list.

String example: "250 350". There could be any number of elements and the values could be integer or float.

What is needed is to subtract a value for each element and the result is still a single string.

Example: Say we want to subtract 9.5 from each element.

input -> "250 350"

output -> "240.5 340.5"

This is what I came up with and it works fine but it feels a bit ad hoc. Wondering if there could be a better solution.

myString = "250 350"

numList = mapcar( 'evalstring parseString(myString)) ; returns (250 350)

adjustedList = foreach(mapcar x numList x-9.5) ; returns (240.5 340.5)

myNewString = buildString(foreach(mapcar x adjustedList sprintf(nil "%g" x))) ; returns "240.5 340.5"

The above works but would like to see alternative methods

Parents

  • A cleaner way of setting numList would be this:

    numList=linereadstring(myString)

    and I would probably use lsprintf instead of sprintf since you only want the return value:

    myNewString = buildString(foreach(mapcar x adjustedList lsprintf("%g" x)))

    (potentially using %N rather than %g because in case the result of your operations were integers; can't be in this case because of the subtraction of a floating point, but that's more general).

    Other than that, it's pretty reasonable. The main difference is really using linereadstring as there's no need to involve the evaluator in this. I am always wary of using evalstring or eval when parsing arbitrary strings - for efficiency but also imagine what happens if myString was "exit() 3"?

    Andrew

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  • A cleaner way of setting numList would be this:

    numList=linereadstring(myString)

    and I would probably use lsprintf instead of sprintf since you only want the return value:

    myNewString = buildString(foreach(mapcar x adjustedList lsprintf("%g" x)))

    (potentially using %N rather than %g because in case the result of your operations were integers; can't be in this case because of the subtraction of a floating point, but that's more general).

    Other than that, it's pretty reasonable. The main difference is really using linereadstring as there's no need to involve the evaluator in this. I am always wary of using evalstring or eval when parsing arbitrary strings - for efficiency but also imagine what happens if myString was "exit() 3"?

    Andrew

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