How do I remove an item from a list?

Rosebud · 04-23-2021 05:24 PM

How do I remove an item from a list? For example, lets say I have a list {2,4,4,1,9,3}. How can I remove only one of the 4’s from the list? Or, how could I remove item #3 from the list? I can’t use list subtraction because it removes both 4’s from the list.

Steve

Suvrutt_Gurjar

Both the examples you have shared are related to the number 4 in the list that appears twice in the list. So could you update if you are trying to remove an item at a specific position in a list or are you trying to remove duplicates from the list?

If you wish all the duplicates removed from a list, please use UNIQUE() function.

If you wish to remove an item at a specific position( index) from a list , you could construct an expression with the INDEX() function.

Please post back if you are looking for something else.

Rosebud

Thanks for the quick reply! I know the index of the item I want to delete from the list. So what would be the the formula to return the list with that item removed?

Suvrutt_Gurjar

With index used, if the item is duplicate, the order of the remaining item in the list will be disturbed. Meaning if list is {2,4,4,1,9,3} and 4 at position 3 needs to be removed, the result will look like {2,1,9,3, 4}

Will it do?

Rosebud

Yes, that would be fine. I am going to sort the list after the item is removed anyway.

Suvrutt_Gurjar

Sorry that I did not ask a question earlier. Is you main intention to remove duplicates or a single element at some known index position. And if there are duplicates , how many times a duplicate can occur> Is it only twice or more than that?

Rosebud

Could be more than that.

Suvrutt_Gurjar

Thank you. I( believe there is no trivial way to achieve what you are looking for. If I come across a solution, I will post.

Rosebud

Ok. Thanks Suvrutt!

Suvrutt_Gurjar

Have tried to put an expression together, a bit longish. It could be possibly further optimized, but the following works even with lists having duplicates per my basic testing. Please test well.

IF(LEN(TEXT([NumberList V]))-(LEN(TEXT(TOP([NumberList V], [IndexPosition])))+2)<0,TOP ([NumberList], [IndexPosition]-1),
TOP ([NumberList], [IndexPosition]-1) + SPLIT(RIGHT([NUMBERLIST V] , LEN(TEXT([NumberList V]))-(LEN(TEXT(TOP([NumberList V], [IndexPosition])))+2)),","))

In the above expression [IndexPosition] is Number Type column. Denotes the position of the number that needs to be removed from the list.
[NumberList] is a column type enumlist with base type as number. Something like {2,4,4,1,9,3}. that you have shared. [NumberList] is presumed to create a list in the AppSheet standard format , meaning {1, 2 , 3 , 4 , 5} -There is a space between number and next and previous commas.

The expression removes a number or item from the [NumberList] column at the position denoted by [IndexPosition]

Edit: Expression changed to take care of some edge conditions.

Rosebud

Thanks! I will try it out and work with it.