Build array of elements in a for loop

Hello, I have a program where I am taking voltage measurements and computing resistances inside of a for loop. I then want to take these values an place them in individual arrays which are then sent to another subVI to compute the mean and standard deviation. Currently it appears the arrays are getting overwritten and only one value is stored in the array. Please let me know what I have to do to fix this. Thank you.
I have attached my VI and the area I am talking about is in the case statement inside the big for loop for case 1.
Message Edited by BJalbert on 05-25-2007 09:57 AM
Attachments:
StdTest2.vi ‏159 KB

The image shows two possibilities:
Still, you should really simplify your data structures. For example you could have all your 7 results as a single 1D array and built it as a 7xN 2D array, etc. You probably can reduce the clutter on the diagram by 90%!
It is a nightmare to deal with subVIS containing so many individual connectors.
Message Edited by altenbach on 05-25-2007 08:24 AM
LabVIEW Champion . Do more with less code and in less time .
Attachments:
ArrayBuildingInLoop.png ‏5 KB

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Real-time updates of an XY graph with a 2D array (x,y) inside a for-loop

Hi all,
I am new to this forum, and relatively new to LabView (I've used TestPoint in the past), and I have a question. I have implemented a for-loop to grab data from an LCR meter (via GPIB) which becomes the Y data. The X data is calculated and tunneled into the for loop (although varies with incrementing 'i'). Anyhow, I am trying to store all of the data and keep the user updated throughout the test by plotting the XY Graph each iteration. Right now, the XY Graph plots one point at a time, so somehow the data I am appending to the 2D array (x,y data) is getting overwritten each itteration. How can I make it so that each new point is added to the array, making it bigger so that the data will be saved and so that the user will be able to see all the data in real-time on the graph as the test in running?
Thanks
P.S. I would post a screenshot, but I'm not sure how to upload here.

Hey Mendeleev3104,
There is an attachment section at the bottom of the post when creating or editing a post. You might want to use that to attach a picture of your code.
None the less I will give a shot with some suggestions without viewing your code.
You should look into using shift registers along with the Insert Into Array.vi to build an array of numbers. A good source of information for shift registers can be found in the For Loop and While Loop Structures help.
Hopefully this helps!!
Aashish M
Applications Engineer
National Instruments
http://www.ni.com/support/

How to index a array to give it to for loop for one value at a time sequence to be ensured

I need to give one number from a array at a time to a for loop. means the for loop have to execute one number at a time from a array of numbers. How to do it

Ranjeet,
Ranjeet_Singh wrote:
But question is same only. is in it ?
With all due respect, NO.
Please make sure you know what you are talking about before blatantly countering someone else's comment. Can you prove that your vi and TiTou's snippet will do the same thing?
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Updating sceen elements in a for loop?

Hi
I have a for loop that, among other things, contains an appendText command. It adds a character to a text box on the screen.
I notice that rather than append the text on each iteration, it waits until the for loop has finished, and then appends all the characters.
It's not noticable on short loops, but very noticable on longer ones.
Is there a way to make flash update the text box as each iteration happens, rather than dump all the appended text at the end?
Thanks guys.
Shaun

Hi Kenneth
I've been playing around with that this afternoon, and am making progress, but was wondering if you could please explain it a little with regard to my code?
The function I want to have a graphical progress on is populateOutputBox(). Basically, it's taking data from an array (songlist), adding text to each array item, appending the result to a text box, and then the save function saves the data from the text box as a txt file.
It was working fine as a for loop, but as you've shown, no screen updates could happen if a lot of data is being processed.
So I've changed populateOutputBox to do one iteration, and on each check if the array has been iterated through.
Here's that code, followed by the code I've taken from your tut for checking on each frame:
function populateOutputBox() {
   //blah blah code for adding text to array items, then...
    p = p + 1;
    if (p == songlist.length)
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function startFunc() : void {
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    //populateOutputBox();
function onCycle( event : Event ) : void {
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       cycle = populateOutputBox();
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As it stands, Flash seems to do nothing when I run it. Am I supposed to initiate populateOutputBox(); in the startFunc(), or does that happen automatically in the onCycle func?
Thanks again Kenneth.

How to avoid Build Array function inside a For (while) Loop?

Hi there,
I have a simple question about how to avoid using Build Array function inside the loop. Now I want to remove the Build Array funtion inside the loop to improve the performance (To get better memory management). Any idea how to do that?
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Warmest regards,
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It's been my experience that using the auto-indexing to build an array
on a For loop is just as good as initializing and replacing elements.
The For loop knows before it runs how many iterations it has to run and
can allocate the array ahead of time.
You're better off initializing and replacing when using a While loop
because it does not know how many iterations it will run and can't
pre-allocate the array ahead of time.
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Build 1D array using for loop

Hi guys,
I am testing out array. How do I create a 1D array of x-y using for loop?

Nextal wrote:
I am testing out array. How do I create a 1D array of x-y using for loop?
OK, first of all you did not say what the array should contain. If you want an array that has one array element for each iteration of the while loop, you need to first think a bit harder. Your outer loop has no wait, thus it will spin millions of times per second and you will run out of memory soon, no matter how much memory you have. How many times should the while loop iterate? If you know the number before the program starts, you would use a FOR loop and autoindex at the loop boundary.
If you want to use a whiile loop, you need a mechanism to keep the array size reasonable. For small final arrays, you can just build the array in a shift register if you need it updated as it happens. If you only need the array after the loop stops, you can autoindex at the right loop boundary.
In any case, you should take a step back and decide what you really want. Currently the specifications are very vague and unreasonable.
LabVIEW Champion . Do more with less code and in less time .

Using a For Loop Index for Array Element Number?

Hi. Thanks in advance for the help. I can't seem to find what I want to do here using the search function... probably because I don't know how to frame the question appropriately. Ignore the title to this post cause it's probably wrong vocabulary for what I want to do.
Here's the situation:
I have a 2D array where the first column is the X data and each subsequent column is Y data (call it Y1...Yn). The n-value varies from run to run (some runs have 4 columns of data, some have 20), but that is easily gathered when reading the data file. I need to perform a number of operations on each set of data, the least of which is smoothing the data and graphing it, so I'm limiting my discussion to these 2 operations.
What I want is a for loop structure where the indexing of the loop tracks the Y1...Yn columns, grabs each column for the iteration, performs the relevant analysis, and spits out the result, but in a stackable manner. Thus the title; I want to use the for loop's index to mark the array element for building a new array.
See the image attached. A 2D array of 9 columns (X, Y1...Y8) is analyzed such that each data set, (X, Y1), (X, Y2)...(X, Y8) is bundled, graphed, run through a B-spline Fit, of which is also graphed. I need to replace this with something that looks like the for loop structure shown.
I just don't know how to get those two data bundles [(X, Yi) and it's smoothed pair] out of the for loop in a stacked set from every iteration of the for loop.
Again the title, I think I want to build a new array where i use the index of the for loop to control the entries of the new array. But I can't see how to do that.
Any help would be appreciated.
Attachments:
NeedForLoopForThis.PNG ‏30 KB

Hello H.R. Dunham, and welcome to the forum!
It seems that you may be looking for Auto-Indexing, a basic feature of loops in LabVIEW. You'll need to transpose your array before wiring it into the for loop, as elements are auto-indexed by row before column, but at that point you should be able to operate on each column and output an array of n cluster elements corresponding to your input columns. Auto-indexing tunnels look like brackets to indicate each element will be indexed automatically- this should be the default when wiring an array into a for loop or when wiring anything out of a for loop.
As for how to build your pairs, I suggest removing the X column and creating a "starter" cluster containing your X data and placeholder Y data before entering your "Y" processing loop. Use the bundle by name function in the for loop to insert your processed column data into the cluster and auto-index the cluster output. Flow would be something like this:
1) Gather data
2) Split X and Y using standard array operations
3) Create "template" cluster with shared X data
4) Pass template cluster and Y-column array into an auto-indexed for loop.
5) Insert processed Y data into cluster inside loop.
6) Auto-index cluster data out of loop.
This tutorial is probably also a good place to get started:
Getting Started with NI LabVIEW Module 3: Loops
http://www.ni.com/white-paper/7528/en/
Hope that helps!
Regards,
Tom L.

Creating an array in a 'for' loop (resetting loop count)

Hi,
I am trying to integrate an acceleration signal coming from a CRIO analogue input to obtain the speed and then further integrate to get the displacement of a vibration system.
I understand that in order to perform the integration, an array has to be fed in. My problem is that I could not buffer the signal in a buffer block as I couldn't find any buffer blocks. so I decided to create my an array of data using a 'for' loop. The 'for' loop nests inside a timed loop. The problem that I got stuck at is how to reset the 'for' loop in order to refill the buffer again at every iteration of the outer timed loop.
I have attached the code if that helps. Note that I am using labview 2013.
I would be gratefull if someone who had encountered a similar issue before can help me.
Regards
Ali
Solved!
Go to Solution.
Attachments:
acc_test.vi ‏42 KB

Dear Altenbach,
Many thanks for your reply.
I need to make it clear that I have not had enough hands-on with labview, I have only used it for sometime in the past and now I have to in order to perform some active damping on a 50Hz running machine. I must stress the fact that what i find more intuitive to do in a different programming language (matlab or C) is not as straightforward in labview. so please bear with me if my code has basic mistakes .
All what i am trying to do is obtain the speed and position from an acclerometer signal. unfortunately i dont have a position sensor so i have to measure acceleration then perform time integrations in order to obtain the speed and position respectively. I am using a compact Rio (later in FPGA mode) to take physical measurements of acceleration from the vibratory machine and where i managed to do this bit successfully. when it came to performing the integration, i had to create an array inside my timed loop since i couldn't find a buffer block. I implemented a 'for' loop inside a timed loop in order to build the array. however i got stuck at resetting the count of the 'for' loop in order to refill the array with new values at every new iteration of the outer timed loop. unfortunately, even a sensible answer has been suggested before, i dont seem to have been capable of doing it yet. I really spent all my day trying to figure a way out but not achieved it yet, nevertheless I have learnt many many things by playing around.
I would be gratefull if you could comment on a possible way of doing what i am trying to do.
Kind Regards
Ali

Row operation on array with a For Loop

Hi,
I'm working with a large one dimensional column array. I'm trying to do the following
for i=1:size(A)/2
B(i,: ) =A(1+(i-1)*2:i*2)
So, for example if
A=
0
1
2
3
4
5
6
7
then
B=
0 1
2 3
4 5
6 7
My approach was to use an array subset block inside the for loop to select a number of elements but I'm not sure how to transpose the selected elements into a new row to create the new array B. Is there a more straightforward approach?
Thanks,
Mike
Solved!
Go to Solution.

try experimenting with the reshape array feeding it your input array and re-sizing it to output a 2d aray. It is much faster than using a For loop becuase the data never gets moved and LV just changes the array dimensions and updates the stride.
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Need to access parent elements in nested for-each loop

Hi All,
I have a xslt mapping requirement in which I am completely stuck. The details are as listed below. Please help!
Schema structure is as follows:
Root
Payload
Transaction-123
Loop-LINE
Loop-SDPP
Segment-FSTT
Element-111
Required xslt file structure is:
<xsl:for-each Loop-LINE>
<tns:Item>
<Line-1000>
<Line-2000>
<Line-3000>
<Line-8000>
<xsl:for-each Loop-SDPP>
<xsl:for-each Segment-FSTT[ns0:Element-111 != "A"]>
<SDetails>
</SDetails>
<xsl:for-each Loop-LINE> --------- How to access Loop-LINE element from this for loop????
<tns:Item>
<2000>
<2020>
<2070>
<2150>
</tns:Item>
</xsl:for-each>
</for-each>
</for-each>
</tns:item>
</for-each>
Need help in understanding how can I run a for-each loop for Loop-LINE which is two levels up in the schema tree structure.
Thanks..

Thanks for this answer but I can't obtain the right output with my test case; the multi column must be in the loop as that :
ALPHABETICAL INDEX C1
Alternator .......................................... Feed Pump
Belt Details / Engine Gaskets Sets ..... Flywheel Housing
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INDEX ALPHABETIQUE C2
Alternateur......................................... Culbuteurs
Bloc-Cylindres.................................... Demarreur
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Arrays dimension changed by "for loop"

When using a two(multi)-dimension array as input to a "for loop", the connection
changes inside the loop to a 1D array automatically. Why?!?
I want to perform the same procedure on each subarray of the basic two-dimension
array, by specifing an index. The second dimension I disable indexing. The
index itself can be the for loop index. The problem is the change in connection
between out and in of the for loop.

The question is that you have indexing enabled in the for
loop entry, and the for loop will convert your 2D array in
the necessary number of 1D arrays to be completed in the
for loop. This is good when you don't know how long the
array is going to be, but if you don't like it, you can
right click on the input tunnel and disable indexing.
Hope this helps.
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? on How to Load Variable Within For Loop

Hello,
I'm a PL/SQL newbee so I apologize up front if this is a basic question. In summary, I'm trying to build a field name within a FOR LOOP and also load this field with it's associated data from an input record and finally load the data to the output record and pipe the row. I can successfully build the field name but don't know how to load it with data from the input record.
Here is a sample from the code.
The input table is shown with the 6 different Fnma codes. Instead of checking each code for data, I want to build the field name, load this field name with data from the input record and move the data to the output record.
CURSOR cur_loan(prod_date_in IN DATE) IS
Select
Ln.Ln_No,
Ln.Prod_Date,
Ln.Ln_Fnma_Ftr1_Cd,
Ln.Ln_Fnma_Ftr2_Cd,
Ln.Ln_Fnma_Ftr3_Cd,
Ln.Ln_Fnma_Ftr4_Cd,
Ln.Ln_Fnma_Ftr5_Cd,
Ln.Ln_Fnma_Ftr6_Cd,
from LOAN Ln
where PROD_DATE = '16-FEB-11';
Here is the FOR LOOP that successfully builds the field name in l_feat_code_name. Then I "assume" by moving this field to l_output that l_output will contain the actual data, not the field name. However, it appears to contain the field name instead of the data.
FOR l_To IN 1 .. 6
LOOP
l_feat_code_name := ('l_loan_rec.ln_fnma_ftr'||l_to||'_cd');
l_output := l_feat_code_name;
IF (l_output is not null or
l_output <> ' ') THEN
l_out_rec.Inv_Type := l_Fnma_Cd;
l_out_rec.feat_code := l_output;
l_out_rec.Src_Delete_Flag := l_src_delete_flag_n;
PIPE ROW(l_svc_ln_rec);
END IF;
END LOOP;
How can I move the data itself into the l_out_rec.feat_code output record? Thanks in advance.

Hi,
l_output is defined as follows:
l_output varchar2(20) ;
I appreciate your example.
Again, after I build l_feat_code_name it contains the column name from the input record, Ln_Fnma_Ftr1_Cd, ....Ftr2...., .....Ftr3..... and so on up to Ftr6. However, I also need the **data value** of Ln_Fnma_Ftr1_Cd, ....Ftr2...., .....Ftr3..... and so on up to Ftr6. My question is how to get the data value. You see below when I move l_feat_code_name to l_output I'm expecting l_output to contain the **data value**. Instead, when I display it in DBMS_output, it shows the column name.
CURSOR cur_loan(prod_date_in IN DATE) IS
Select
Ln.Ln_No,
Ln.Prod_Date,
Ln.Ln_Fnma_Ftr1_Cd,
Ln.Ln_Fnma_Ftr2_Cd,
Ln.Ln_Fnma_Ftr3_Cd,
Ln.Ln_Fnma_Ftr4_Cd,
Ln.Ln_Fnma_Ftr5_Cd,
Ln.Ln_Fnma_Ftr6_Cd,
from LOAN Ln
where PROD_DATE = '16-FEB-11';
Here is the FOR LOOP that successfully builds the field name in l_feat_code_name. Then I "assume" by moving this field to l_output that l_output will contain the actual data, not the field name. However, it appears to contain the field name instead of the data.
FOR l_To IN 1 .. 6
LOOP
l_feat_code_name := ('l_loan_rec.ln_fnma_ftr'||l_to||'_cd');
l_output := l_feat_code_name;
IF (l_output is not null or
l_output ' ') THEN
l_out_rec.Inv_Type := l_Fnma_Cd;
l_out_rec.feat_code := l_output;
l_out_rec.Src_Delete_Flag := l_src_delete_flag_n;
PIPE ROW(l_svc_ln_rec);
END IF;
END LOOP;

Slow "for loop"

Hi All,
I am filling a 512x512 array using a couple of for loops which is really slow. I have an initialized array outside and I am using the "replace array subset" as I have heard that this is the fastest way of doing it. In the picture there is an outer third loop which is just the number of arrays to be filled but as it takes 1-2 minutes to complete the inner 2 loops the uoter loop is not the problem.
Any help would be most appreciated.
Thanks
Attachments:
slow array.JPG ‏179 KB

Now i haven't tried this myself, but you've disabled indexing of the matrix. Isn't the whole idea to use the autoindex to make it easier to replace?
/Y
LabVIEW 8.2 - 2014
"Only dead fish swim downstream" - "My life for Kudos!" - "Dumb people repeat old mistakes - smart ones create new ones."
G# - Free award winning reference based OOP for LV

Building an array from a for loop.

Hi all
I have a vi which reads from a file and manipulates the data using for loop. I am taking each element and multiplying it with a constant and converting it to I32. I would like to build back to a new array with the new values. I have attached the vi and a sample data file to read from.
Please suggest if there are any better ways to do this.
Thank you.
Solved!
Go to Solution.
Attachments:
file_read.vi ‏11 KB
file_read.txt ‏1 KB

You can multiply the array with the constant and use the array instead of multiplying it with each element.
The best solution is the one you find it by yourself

Methods to build an array inside a For Loop.

Let me introduce to you my nested For Loops:
They output a 2D boolean array depending on two 1D boolean arrays of different lengths. This is all well and good however, in another part of my program, I want this to be a 1D array instead.
Idea #1:
"I'll just reshape the array at the end. Simples!"
Idea #2:
"Hang on, why am I using three primitives outside the loop when I can use just one inside it along with a shift register?"
Idea #2.5:
"Oh, wait... I remember reading somewhere about continuously building an array (with concatenate inputs) inside a loop being a bad thing and quite slow. Let me test this."
Spoiler (Highlight to read)
Idea #3:
"Umm... okay, so actually the second way is faster. I think if I initialize the shift register first then replace subsets of the array, that might also be better."
Spoiler (Highlight to read)
Idea #4:
"Yep - seems much better. (Something to do with LabVIEW not having to constantly allocate more memory on every iteration of the loop) Looking at this closer, I don't actually need the inner For Loop because of the way I'm handling the arrays. Try again...!"
Spoiler (Highlight to read)
Conclusion(?) #1:
"Well I seem to have arrived at something that looks messier, but executes about 6x faster than my initial idea. That said, the difference rapidly increases as the input arrays get much bigger (becoming orders of magnitude different)."
Is this the most efficient way of doing what I want? Or is there something even better (and works in LV 8.5)?
Never say "Oops." Always say "Ah, interesting!"

Thank you both for the feedback. It never occurred for me to recheck the logic after I'd initially extracted the nested For Loops, but the AND gate output is obviously the same now that it's been pointed out!
Continuing on with Idea #4, I replaced the Select with an AND then compared the times. (also meant I didn't have to initialize one of the arrays anymore)
Spoiler (Highlight to read)
It appears that the AND gate was slower but then I tried with different sizes of initial arrays and in one case, the timings were 'reversed'.
This only happened when the top array (the one that is fed into the AND gate whole) was reduced to a length in the region of 5 elements long.
Spoiler (Highlight to read)
Why does this happen? Is it something to do with the AND gate possibly being optimised for single element operations so smaller arrays are handled better...?
Never say "Oops." Always say "Ah, interesting!"

Build array of elements in a for loop

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