How to detect if a character is an integer, or not.

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Posted on 9 Oct 2020 17:34:14 by martinav

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I need to check if the first character of a string is a number. Is there an easy way to do this? I need to do this in an expression. Some languages have IfError() to trap an error, or some other way?

This is what would work for me (if the error statement was available)

if(IfError(int(substring(item()?['ProductID'],0,1)),0,1)

What I do NOT want to do (but would work):

if(equals(substring(item()?['ProductID'],0,1),'0'),1, 
 if(equals(substring(item()?['ProductID'],0,1),'1'),1,
 if(equals(substring(item()?['ProductID'],0,1),'2'),1,
 if(equals(substring(item()?['ProductID'],0,1),'3'),1, 
 if(equals(substring(item()?['ProductID'],0,1),'4'),1, 
 if(equals(substring(item()?['ProductID'],0,1),'5'),1, 
 if(equals(substring(item()?['ProductID'],0,1),'6'),1, 
 if(equals(substring(item()?['ProductID'],0,1),'7'),1, 
 if(equals(substring(item()?['ProductID'],0,1),'8'),1,
 if(equals(substring(item()?['ProductID'],0,1),'9'),1,
 0))))))))))

Thanks.

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Answers (1)

Clifferton 94 on 01 Dec 2021 at 22:07:38

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Re: How to detect if a character is an integer, or not.

If the 'firstyVAR' block fails, does the flow show a failure in the run history, or is that failure mitigated by the fact that there's a block set to run after a fail?
eliotcole 4,218 Super User 2025 Season 1 on 25 Apr 2021 at 18:18:01

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Re: How to detect if a character is an integer, or not.

I realise that you have a solution, but without getting into the deeper expression and just looking at your initial question, I initially thought of two methods:
Use OR - Potentially simplify your method, firstly by making it easier to parse (visually) with a variable defining the first character separately 'firstyVAR'. Then using OR to simplify your IF tree (these are set as strings for simplicity's sake): or(equals(variables('firstyVAR'), '0'),equals(variables('firstyVAR'), '1'),equals(variables('firstyVAR'), '2'),equals(variables('firstyVAR'), '3'),equals(variables('firstyVAR'), '4'),equals(variables('firstyVAR'), '5'),equals(variables('firstyVAR'), '6'),equals(variables('firstyVAR'), '7'),equals(variables('firstyVAR'), '8'),equals(variables('firstyVAR'), '9'))
Check the first character against an array, which is easier than you'd think, with a pre-set array of ["1","2","3","4","5","6","7","8","9","0"] and then performing a contains(variables('arrayVAR'), variables('firstyVAR')) expression which will return true or false dependent on the number. It's much cleaner.

However, it was in the processing of that second one, that I realised that there's a super easy way to ascertain this:

Run After

So ... Here is the flow that I used to do it (triggerBody()['text'] is where your initial string would be):
ignore the comment in 'intYnVAR'

In order for this to work, everything depends on what happens when defining the integer variable, 'firstyVAR'. So when using the int() conversion function on the first letter of the string:
int(substring(triggerBody()['text'], 0, 1))
That is were you will branch:
For success, if the substring managed to convert into an integer, winner winner chicken dinner.
For failure, if it failed, then this is where you process the failure.
When managing failure states, I always find it simpler to set a boolean, which we can use to move on from there. But you can perform whatever you like, obviously.

The key here is clicking the dot menu on the failure branch and setting the 'Configure run after' value:
Configure run after

Here you ensure that you set it to "has failed".
has failed

Then when the int() runs, if it fails, then the failure branch will run!

You're not done yet, though, as your next entry has to run after EITHER of the previous branches ran. So you need to repeat the action on the unifying connector. You must go in twice to get it right, though:
Once to set it to run after any eventuality in the success branch. CLICK 'Done'
Once more to set it to run after any eventuality in the failure branch. CLICK 'Done'
Once more with feeling

That's it!

Here's some results for proof:
no integer

integer

NB - Be careful with 'Run after' as it has a knack of removing itself when you amend affecting parts of the flow. So always check your Run Afters if you have them! (or try to get them in a scope)
Verified answer

martinav 3,340 on 10 Oct 2020 at 14:26:53

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Re: How to detect if a character is an integer, or not.

I gave up on this. Ended up changing the View in SQL. It has proper command statements for such things.
CASE WHEN (dbo.OrderDetail.OrderNumber LIKE 'Kel%') THEN 2 ELSE CASE WHEN (dbo.OrderDetail.OrderNumber LIKE 'RMA%') THEN 3 ELSE CASE WHEN (dbo.OrderDetail.OrderNumber LIKE 'DC%') THEN 5 ELSE CASE WHEN (dbo.OrderDetail.OrderNumber LIKE 'NW%') THEN 5 ELSE CASE WHEN (dbo.OrderDetail.OrderNumber LIKE 'BT%') THEN 5 ELSE CASE WHEN (dbo.OrderDetail.OrderNumber LIKE 'DC%') THEN 5 ELSE CASE WHEN (dbo.OrderDetail.OrderNumber LIKE 'HF%') THEN 5 ELSE CASE WHEN (ISNUMERIC(SUBSTRING(dbo.OrderDetail.ProductID, 1, 6)) = 1) THEN 4 ELSE CASE WHEN (ISNUMERIC(LEFT(dbo.OrderDetail.ProductID, 1)) = 1 AND SUBSTRING(dbo.OrderDetail.ProductID, 2, 1) = '-') THEN 5 ELSE CASE WHEN (LEFT(dbo.OrderDetail.ProductID, 1) = 'K' AND ISNUMERIC(SUBSTRING(dbo.OrderDetail.ProductID, 2, 4)) = 1) THEN 4 ELSE 1 END END END END END END END END END END AS OrderType
martinav 3,340 on 09 Oct 2020 at 18:52:28

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Re: How to detect if a character is an integer, or not.

Yea, the action block method is great, but will not work in this case, because this statement is with a Select action. I was going to be happy with the nested if(), which worked great for one condition. However, now I have the need to detect if the first SIX characters of a string constitute a number. That will break the lexicographical order idea. Which was a good one, btw. But things have become more complex.

What I am actually doing, is moving this condition statement to create another data column in a Flow Select action. This is the statement in powerapps:

If(StartsWith(OrderNumOB,"Kel"),2, StartsWith(OrderNumOB,"RMA"),3, StartsWith(ProductID,"HF"),5, StartsWith(ProductID,"DC"),5, StartsWith(ProductID,"NW"),5, IsMatch(ProductID,Match.Digit) And Mid(ProductID,2,1)="-",5, StartsWith(ProductID,"BT"),5, StartsWith(ProductID,"K") And IsNumeric(Mid(ProductID,2,1)),4, IsMatch(ProductID, Match.Digit & Match.Digit & Match.Digit & Match.Digit & Match.Digit & Match.Digit),4,1)

This is what I have so far in an expression. This works perfectly at this point. However, I need to add the last two lines from above, into the expression.

if(startsWith(item()?['OrderNumOB'],'Kel'),2, if(startsWith(item()?['OrderNumOB'],'RMA'),3, if(startsWith(item()?['ProductID'],'HF'),5, if(startsWith(item()?['ProductID'],'DC'),5, if(startsWith(item()?['ProductID'],'NW'),5, if(startsWith(item()?['ProductID'],'BT'),5, if(and( equals( if(equals(substring(item()?['ProductID'],0,1),'0'),1, if(equals(substring(item()?['ProductID'],0,1),'1'),1, if(equals(substring(item()?['ProductID'],0,1),'2'),1, if(equals(substring(item()?['ProductID'],0,1),'3'),1, if(equals(substring(item()?['ProductID'],0,1),'4'),1, if(equals(substring(item()?['ProductID'],0,1),'5'),1, if(equals(substring(item()?['ProductID'],0,1),'6'),1, if(equals(substring(item()?['ProductID'],0,1),'7'),1, if(equals(substring(item()?['ProductID'],0,1),'8'),1, if(equals(substring(item()?['ProductID'],0,1),'9'),1, 0)))))))))), 1), equals(substring(item()?['ProductID'],1,1),'-')),5, 0))))))
efialttes 14,756 on 09 Oct 2020 at 18:16:35

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Re: How to detect if a character is an integer, or not.

@martinav

Mmmm... to trap errors in power automate you need to implement a try-catch action blocks based approach.

https://poszytek.eu/en/microsoft-en/office-365-en/powerautomate-en/try-catch-pattern-in-microsoft-flow/

I don't believe it is possible to implement it by means of a pure expression based approach, but if someone else has managed to do that, more than happy to learn one more thing

Now, just guessing if a lexicographical order based expression I.e. the first character is greater or equal to character '0' and less or equal to character '9' is could help you to achieve your requirements

Hope this helps