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Hash or checksum for data entry

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Posted on by EdHansberry

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I am going to be building an app that will have some data keyed in from another source. In order to minimize or eliminate keying errors, I'd like to have a hash or checksum for each row of data. I can get that done at the source too.

So if data looks like this:

Item Number

Month 1 Units

Month 2 Units

Month 3 Units

Entry Date

Checksum

Doing a checksum on values is easy. How would you suggest I approach getting a checksum to include the item number, which is an alphanumeric string? In VBA I'd just get the length, then loop through it one char at a time and get the ASCII number of the character then do some math with the other numeric values in the row to get a probably unique value that would prevent entry errors.

But Power Apps doesn't support FOR/NEXT loops like that. Other ideas? The item numbers aren't a consistent length so I cannot just parse it out to 10 chars or something and do it that way. It may be between 5 and 12 chars.

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mdevaney 29,991 Moderator on at

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@EdHansberry

I feel like it might be easier to answer this question if we had a practical example to work from here.

Can you give some sample inputs?

What does the checksum process look like? Give an example with pseudocode or VBA.

What is the output?

I have found it possible to create both FOR NEXT and DO WHILE loops in PowerApps so hopefully what I know can be applied to your app. A good mathematical problem or PowerApps hacking challenge is always fun 🙂

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EdHansberry 386 on at

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Item Number Month 1 units Month 2 Units Month 3 Units Date
12345AB-R13 1000 2000 1500 Mar-31-2020

I haven't worked out my math yet but for simplicities sake I might do the following

Month 1 units * Square Root(Month 2 units) / Month 3 units
Take the integer portion of that number and halve it.
Add the fractional portion of the date divided by pi
Take the first 8 digits of the fraction and convert to an integer ( * 10000000) and add that to the integer portion of that.
Convert that numeric string to text, and just use the last 5 digits.

That would give me a simple 5 digit number to key in that would be hard to replicate with wrong data. But I need to work in the item number (alphanmeric) somehow.

Make sense? I'd be happy if I could get the ASCII code of each char of the number and just use the first digit from each and construct another 5-12 digit integer to add to the above before I extracted the last 5 digits.

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mdevaney 29,991 Moderator on at

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@EdHansberry
Is the fundamental problem obtaining the ASCII code of each char of the Item Number?

This is the code I used:

//Char codes for 0-9 A-Z a-z Set(charCodesAlphanumeric,[48,49,50,51,52,53,54,55,56,57,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122]); //Initialize collections ClearCollect(myItemNumber, Split("12345ABR13","")); ClearCollect(mySolution, {Char: "", CharCode: 0}); Clear(mySolution); //Loop to find Char codes ForAll(myItemNumber, ForAll(charCodesAlphanumeric, If(Char(Value) = Result, Collect(mySolution, {Char: Result, CharCode: Value})) ) )

Resulting in the collection mySolution:

Char code reference here (instead of ASCII):

https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/functions/function-char

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EdHansberry 386 on at

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Thanks @mdevaney. That is super helpful. Definitely gives me a path forward.

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mdevaney 29,991 Moderator on at

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@EdHansberry

You always ask such interesting questions Ed. This time was no different. I could not resist!

Now I know who to ask if I need help with making a checksum algorithm. You seem to be very keen on the subject 🙂

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