topic insert into array doesn't work in LabVIEW

insert into array doesn't work

wb2nvy — Wed, 21 May 2008 20:31:18 GMT

Please see attached screenshot & VI. I want to take a 1D array and break it into a 2-column array. The VI I have written works exactly right the FIRST time I run it. It puts the data in columns 0 and 1. The SECOND time I run it, it places the data into columns 2 and 3. Why does it do this? Since I hardwired the column index to 0, I expect it to OVERWRITE the first run of data and keep putting it into column 0 (and 1).

Re: insert into array doesn't work

MikeS81 — Wed, 21 May 2008 20:33:27 GMT

Hi wb2nvy,
where is your attachment?
Mike

Re: insert into array doesn't work

ShotSimon — Wed, 21 May 2008 20:34:39 GMT

Halarious. -SS

Message Edited by ShotSimon on 05-21-2008 03:34 PM

Re: insert into array doesn't work

wb2nvy — Wed, 21 May 2008 20:33:59 GMT

I thought I attached jpg and vi but I guess I didn't. Here they are... I hope.

Re: insert into array doesn't work

wb2nvy — Wed, 21 May 2008 20:35:08 GMT

Only 1 attachment stuck. Here's the other one.

Re: insert into array doesn't work

MikeS81 — Wed, 21 May 2008 20:38:34 GMT

Hi wb2nvy,
insert into, means that you insert new data into existing one, so you insert everytime your two arrays into your existing array with start at the first row.

Hope it helps.
Mike

Re: insert into array doesn't work

wb2nvy — Wed, 21 May 2008 20:44:00 GMT

I half understand your answer Mike. I agree it should INSERT into the array the new data, BUT shouldn't it insert it where I TELL IT to insert it, which is starting at COLUMN 0, not ROW 0. I wired the COLUMN index to 0.

Re: insert into array doesn't work

smercurio_fc — Wed, 21 May 2008 20:53:50 GMT

The behavior you're seeing is due to the fact that you're using a local variable. The first time you run the VI the indicator is empty. The local variable returns an empty array. You run the VI, now the indicator has values. You run the VI again, now the local variable returns the values that are already there from the previous run.

If you're trying to convert a 1D array to a 2D array, why don't you just use the Reshape Array function?

Message Edited by smercurio_fc on 05-21-2008 03:53 PM

Re: insert into array doesn't work

wb2nvy — Wed, 21 May 2008 20:58:53 GMT

Yes I can use reshape array, but I still want to understand why Insert into array doesn't work. Even if I am using the local variable, I am TELLING the VI to put my data at column 0, regardless of what may already appear there by virtue of the local variable. Should the help file for Insert into array say something like "data will be inserted where you wire the index, UNLESS there's already data there, then all bets are off"?

Re: insert into array doesn't work

Dennis_Knutson — Wed, 21 May 2008 21:09:27 GMT

I don't understand what the confusion is about. Run the VI once, then change your array constant to something else. You will see those new values in columns 0 and 1.

Re: insert into array doesn't work

smercurio_fc — Wed, 21 May 2008 21:11:13 GMT

What makes you think the Insert Into Array is not working properly and that data is being put into columns 2 and 3 on the second run? If you run the VI a second time with different values for the input array you will see that the Insert Into Array is operating properly. The attached modication is in essence doing this:

Insert into array is insert, not overwrite. If you want it to overwrite, use Replace Array Subset.

Message Edited by smercurio_fc on 05-21-2008 04:11 PM

Re: insert into array doesn't work

ShotSimon — Wed, 21 May 2008 21:35:13 GMT

Dennis,

I can understand wb2nvy's confusion. When I originally ran the vi it looked like the index was moving the data higher and higher into the array. When in fact the new data is being pushed to index 0 of the existing array, but since the data looks the same, it gives the illusion as it is being indexed incorrectly. Your suggestion of changing the value removes this illusionJ

On a side note I thought maybe he was looking to split the array at an odd point. This would leave the array in two pieces that are different sizes. Then I started thinking how do you make this re-shape properly? And I came up with the attached solution.

*How do you get the png to appear;)

Regards,

-SS

Message Edited by ShotSimon on 05-21-2008 04:34 PM

Message Edited by ShotSimon on 05-21-2008 04:35 PM

Re: insert into array doesn't work

Mathan — Thu, 22 May 2008 04:54:21 GMT

ShotSimon wrote:

*How do you get the png to appear;)

1) attach the .png file as usual.

2) open the attachment. copy the url.

3) Edit the original post and click "Insert an image" (shown in the attachement)

and paste the url.

4) post it again. achieved ur wish.

Thanks,

Mathan

Message Edited by mathan on 05-21-2008 11:54 PM

Re: insert into array doesn't work

wb2nvy — Thu, 22 May 2008 11:46:58 GMT

Yes Dennis, your suggestion works. NOW explain to me WHY it should work. If I tell the Insert into array to put my data at column ZERO, why doesn't it PUT IT THERE EVERY TIME and overwrite if necessary? And if after filling columns 0 and 1 I then tell it to put data at column 5, WHY DOES IT PUT MY DATA AT COLUMN 0???? It doesn't make sense.

Re: insert into array doesn't work

JeffOverton — Thu, 22 May 2008 11:57:24 GMT

If you want to overwrite data, you need to use Replace Array Subset. If you use Insert Into Array, it will always insert new data and increase the size of your array.

Re: insert into array doesn't work

JeffOverton — Thu, 22 May 2008 12:06:19 GMT

Oh and also, you can only insert into an existing array index. So when you try to insert into column 5, nothing is happening. If you right click on your indicator and select data operations->reinitialize value to default and try to insert at column 5, you'll still have an empty indicator. Basically, insert has to have existing data to put your new data in front of.

Re: insert into array doesn't work

wb2nvy — Thu, 22 May 2008 12:45:22 GMT

ShotSimon- you hit the proverbial nail on the head. You understand my confusion, and you cleared it for me. I now understand my data IS going where I tell it to, and the OLD data is being pushed aside. And I also now know that I can't put data into column 5, for example, without first initializing the array with something. Thank you all very much for your help. I JUST WISH THE N.I. DOCUMENTATION WOULD HAVE SAID THAT & SAVED US ALL SOME TIME AND FORUM SPACE.

Re: insert into array doesn't work

smercurio_fc — Thu, 22 May 2008 14:12:50 GMT

So the example that I provided which clearly showed what was going on wasn't obvious enough? Also, the Help for Insert Into Array says:

Inserts an element or subarray into n-dim array at the point you specify in index.

For the "index" input it says

index 0..n-1 specifies the point in the array at which you want to insert the element, row, column, page, and so on. You can wire only one index input. For example, to insert a 1D array as the fourth row of a 2D array, wire 3 to the first index input, and the second index input becomes disabled. To insert the array as the fourth column of the 2D array, wire 3 to the second index input, and the first index input becomes disabled.

How much more clear than that can you be? It also would be redundant to say that you can't insert into a column that doesn't exist, because ... it doesn't exist! That action is undefined.

Re: insert into array doesn't work

wb2nvy — Thu, 22 May 2008 14:33:53 GMT

smercurio, I'm sorry if I hurt your feelings by not understanding your response. Fact is, you clearly didn't understand what I was trying to accomplish. Your example of using Reshape Array didn't result in what I was trying to do. In fact it CAN'T be done with Reshape Array. If you look at the example I posted, it does not resemble your proposed solution. I attached what I finally found worked, using 2 Array Subsets and a Transpose.

Re: insert into array doesn't work

smercurio_fc — Thu, 22 May 2008 14:41:04 GMT

I wasn't referring to the Reshape Array example. I was referring to the example in post #11 (at the top of this page with a great big figure).

My feelings weren't hurt. I just found it curious that the example clearly showed what you said with "I now understand my data IS going where I tell it to, and the OLD data is being pushed aside."

Whatever. As long as you understand now that Insert Into Array is not broken and that it operates exactly as designed and described.

Also, just to prove to you that Reshape Array does work:

Message Edited by smercurio_fc on 05-22-2008 09:41 AM