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  • Numpy zero rank array indexing/broadcasting

    - by Lemming
    I'm trying to write a function that supports broadcasting and is fast at the same time. However, numpy's zero-rank arrays are causing trouble as usual. I couldn't find anything useful on google, or by searching here. So, I'm asking you. How should I implement broadcasting efficiently and handle zero-rank arrays at the same time? This whole post became larger than anticipated, sorry. Details: To clarify what I'm talking about I'll give a simple example: Say I want to implement a Heaviside step-function. I.e. a function that acts on the real axis, which is 0 on the negative side, 1 on the positive side, and from case to case either 0, 0.5, or 1 at the point 0. Implementation Masking The most efficient way I found so far is the following. It uses boolean arrays as masks to assign the correct values to the corresponding slots in the output vector. from numpy import * def step_mask(x, limit=+1): """Heaviside step-function. y = 0 if x < 0 y = 1 if x > 0 See below for x == 0. Arguments: x Evaluate the function at these points. limit Which limit at x == 0? limit > 0: y = 1 limit == 0: y = 0.5 limit < 0: y = 0 Return: The values corresponding to x. """ b = broadcast(x, limit) out = zeros(b.shape) out[x>0] = 1 mask = (limit > 0) & (x == 0) out[mask] = 1 mask = (limit == 0) & (x == 0) out[mask] = 0.5 mask = (limit < 0) & (x == 0) out[mask] = 0 return out List Comprehension The following-the-numpy-docs way is to use a list comprehension on the flat iterator of the broadcast object. However, list comprehensions become absolutely unreadable for such complicated functions. def step_comprehension(x, limit=+1): b = broadcast(x, limit) out = empty(b.shape) out.flat = [ ( 1 if x_ > 0 else ( 0 if x_ < 0 else ( 1 if l_ > 0 else ( 0.5 if l_ ==0 else ( 0 ))))) for x_, l_ in b ] return out For Loop And finally, the most naive way is a for loop. It's probably the most readable option. However, Python for-loops are anything but fast. And hence, a really bad idea in numerics. def step_for(x, limit=+1): b = broadcast(x, limit) out = empty(b.shape) for i, (x_, l_) in enumerate(b): if x_ > 0: out[i] = 1 elif x_ < 0: out[i] = 0 elif l_ > 0: out[i] = 1 elif l_ < 0: out[i] = 0 else: out[i] = 0.5 return out Test First of all a brief test to see if the output is correct. >>> x = array([-1, -0.1, 0, 0.1, 1]) >>> step_mask(x, +1) array([ 0., 0., 1., 1., 1.]) >>> step_mask(x, 0) array([ 0. , 0. , 0.5, 1. , 1. ]) >>> step_mask(x, -1) array([ 0., 0., 0., 1., 1.]) It is correct, and the other two functions give the same output. Performance How about efficiency? These are the timings: In [45]: xl = linspace(-2, 2, 500001) In [46]: %timeit step_mask(xl) 10 loops, best of 3: 19.5 ms per loop In [47]: %timeit step_comprehension(xl) 1 loops, best of 3: 1.17 s per loop In [48]: %timeit step_for(xl) 1 loops, best of 3: 1.15 s per loop The masked version performs best as expected. However, I'm surprised that the comprehension is on the same level as the for loop. Zero Rank Arrays But, 0-rank arrays pose a problem. Sometimes you want to use a function scalar input. And preferably not have to worry about wrapping all scalars in at least 1-D arrays. >>> step_mask(1) Traceback (most recent call last): File "<ipython-input-50-91c06aa4487b>", line 1, in <module> step_mask(1) File "script.py", line 22, in step_mask out[x>0] = 1 IndexError: 0-d arrays can't be indexed. >>> step_for(1) Traceback (most recent call last): File "<ipython-input-51-4e0de4fcb197>", line 1, in <module> step_for(1) File "script.py", line 55, in step_for out[i] = 1 IndexError: 0-d arrays can't be indexed. >>> step_comprehension(1) array(1.0) Only the list comprehension can handle 0-rank arrays. The other two versions would need special case handling for 0-rank arrays. Numpy gets a bit messy when you want to use the same code for arrays and scalars. However, I really like to have functions that work on as arbitrary input as possible. Who knows which parameters I'll want to iterate over at some point. Question: What is the best way to implement a function as the one above? Is there a way to avoid if scalar then like special cases? I'm not looking for a built-in Heaviside. It's just a simplified example. In my code the above pattern appears in many places to make parameter iteration as simple as possible without littering the client code with for loops or comprehensions. Furthermore, I'm aware of Cython, or weave & Co., or implementation directly in C. However, the performance of the masked version above is sufficient for the moment. And for the moment I would like to keep things as simple as possible.

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  • how Do I list all table names in SQL Server using T-SQL?

    - by shrimpy
    SELECT name FROM sys.databases -- this can list all database name in the server user database SELECT * FROM INFORMATION_SCHEMA.TABLES -- these two line can list the table for one particular database But how can I output the results like below? Database Table --------- ------------- db1 t1 db1 t2 db2 t1 ... ...

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  • Select a particular column using awk or cut or perl

    - by javed abbas
    Have a requirement to select the 7th column. eg: cat filename | awk '{print $7}' The issue is that the data in the 4th column has multiple values with blank in between. example - The last line in the below output: user \Adminis FL_vol Design 0 - 1 - group 0 FL_vol Design 19324481 - 3014 - user \MAK FL_vol Design 16875161 - 2618 - tree 826 FL_vol Out Global Doc Mark 16875162 - 9618 - /vol/FL_vol/Out Global Doc Mark

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  • Python timezone issue?

    - by Timmy
    im having troubles with parsing a feed and getting the time. i am using dateutil.parser from dateutil.parser import parse print updated, parse(updated ), parse( updated ).utcoffset() this should be a time in cali, output 2010-05-20T11:00:00.000-07:00 2010-05-20 11:00:00.000000-07:00 -1 day, 17:00:00 why is the offset -1 day 17 hours? this is causing me issues when i try to do things with it

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  • A quick way to map unordered list of longs to buffer location ?

    - by alhazen
    I have a large number of points (indexed by long) that are processed by multiple threads and I'm using a buffer to hold the output results in order. As the number of points processed is huge, what would be an efficient way to map the indexes of the points to the corresponding ordered position in the buffer ? Example: long bufferIndex bufferIndex index (if BufferSize = 2) (if BufferSize = 4) ---------------------------------------------- 2938 0 0 2939 1 1 2941 1 3 2940 0 2 Thanks.

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  • set/add view from controller action

    - by user359650
    Hi all, I'm trying to set a view script to be executed in addition to the currently requested action view script. I want to do this from the controller action itself in a way that this new view script output will be available from the layout $this-layout()-content helper. I found the setView() method but don't know how to use it from the controller. Thanks a lot.

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  • When using the Auth component with CakePHP, I keep ketting this error. Why?

    - by Josh Brown
    Warning (2): Cannot modify header information - headers already sent by (output started at /Applications/MAMP/htdocs/iframeworking/iframe/app/models/frame.php:7) [COREcake/libs/controller/controller.php, line 647] here is the code from frame.php: <?php class Frame extends AppModel { var $name = 'Frame'; var $belongsTo = array('User' => array('className' => 'User', 'dependent' => true)); } ?>

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  • Apply command to each line

    - by Alex
    Suppose I have some output from a command (such as ls -1): a b c d e ... I want to apply a command (say echo to each one, in turn). E.g. echo a echo b echo c echo d echo e ... What's the easiest way to do that in bash?

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  • problem with mingw32-make

    - by stupid_idiot
    hi, I'm quite new with makefile but I don't think the problem I got is caused by my noobness. Somehow if I try to execute mingw32-make from Users/(user)/Documents/myProject the output is "mingw32-make: *** No targets specified and no makefile found. Stop." if I just drag the folder with it to my Desktop and execute make, it works. Any ideas why does it behave like this or perhaps how to make it work from Documents directory too?

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  • Java NullPointerException. Why?

    - by user292844
    I am new to Java. I just read that class variables in Java have default value. I tried the following program. I was expecting to get the output as 0, which is the default value on an integer, but I get the NullPointerException. What am I missing? class Test{ static Integer iVar; public static void main(String...args) { System.out.println(iVar.intValue()); } }

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  • echo "-e" doesn't print anything

    - by wheleph
    I'm using GNU bash, version 3.00.15(1)-release (x86_64-redhat-linux-gnu). And this command: echo "-e" doesn't print anything. I guess this is because "-e" is one of a valid options of echo command because echo "-n" and echo "-E" (the other two options) also produce empty strings. The question is how to escape the sequence "-e" for echo to get the natural output ("-e").

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  • Why is FF on OS X loosing jQuery-UI in click event handler?

    - by Jean-François Beauchamp
    In a web page using jQUery 1.7.1 and jQUery-UI 1.8.18, if I output $.ui in an alert box when the document is ready, I get [object Object]. However when using Firefox, if I output $.ui in a click event handler, I get 'undefined' as result. With other browsers (latest versions of IE, Chrome and Safari), the result is still [object Object] when clicking on the link. Here is my HTML Page: <!doctype html> <html> <head> <title></title> <script src="Scripts/jquery-1.7.1.js" type="text/javascript"></script> <script src="Scripts/jquery-ui-1.8.18.js" type="text/javascript"></script> <script type="text/javascript"> $(document).ready(function () { alert($.ui); // ALERT A $(document).on("click", ".dialogLink", function () { alert($.ui); // ALERT B return false; }); }); </script> </head> <body> <a href="#" class="dialogLink">Click me!</a> </body> </html> In this post, I reduced to its simplest form another problem I was having described here: $(this).dialog is not a function. I created a new post for the sake of clarity, since the real question is different from the original one now that pin-pointed where the problem resided. UPDATE: IF I replace my alerts with simply alert($); I get this result for alert A: function (selector, context) { return new jQuery.fn.init(selector, context, rootjQuery); } and this one for alert B: function (a, b) { return new d.fn.init(a, b, g); } This does not make sense to me, although I may not be understanding well enough what $ is... UPDATE 2: I can only reproduce this problem using Firefox on OS X. On Firefox running on Windows 7, everything is fine.

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  • Python interpreter with Linux Screen

    - by Unknown
    I was working with Python with a Linux terminal screen. When I typed: help(somefunction) It printed the appropriate output, but then my screen was stuck, and at the bottom of the terminal was "(end)". How do I get unstuck? Thanks in advance.

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  • println in grails gsp file

    - by Srinath
    I know this is simple thing, but i was not aware. I used println in gsp file and expected to print output in console. But this is showing on page. <% for(int i =0; i < threads.size();i++) { println i } % thanks.

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  • Got a question I don't understand, can anyone make sense of it?

    - by user275074
    Question on a on-line resource paper: Create javascript so that the following methods produce the output listed next it. circle = new Circle(); console.log(circle.get_area()); // 3.141592653589793 circle.set_radius(10); console.log(circle.get_area()); // 314.1592653589793 console.log(circle); // the radius of my circle is 10 and it's area is 314.1592653589793 Can anyone understand what is being asked?

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  • MS Access query for time

    - by nisha
    following data and using MS Access with VB6 UserID UserName LogTime LogDate 1 S 9:00 21/5/2010 1 S 10:00 21/5/2010 1 S 11:00 21/5/2010 1 S 12:00 21/5/2010 1 S 14:00 21/5/2010 1 S 17:00 21/5/2010 Need Output as in below 6 columns:- 1 S 21/5/2010 9:00 21/5/2010 10:00 1 S 21/5/2010 11:00 21/5/2010 12:00 1 S 21/5/2010 14:00 21/5/2010 17:00

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  • Android Camera takePicture function does not call Callback function

    - by Tomáš 'Guns Blazing' Frcek
    I am working on a custom Camera activity for my application. I was following the instruction from the Android Developers site here: http://developer.android.com/guide/topics/media/camera.html Everything seems to works fine, except the Callback function is not called and the picture is not saved. Here is my code: public class CameraActivity extends Activity { private Camera mCamera; private CameraPreview mPreview; private static final String TAG = "CameraActivity"; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.camera); // Create an instance of Camera mCamera = getCameraInstance(); // Create our Preview view and set it as the content of our activity. mPreview = new CameraPreview(this, mCamera); FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview); preview.addView(mPreview); Button captureButton = (Button) findViewById(R.id.button_capture); captureButton.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { Log.v(TAG, "will now take picture"); mCamera.takePicture(null, null, mPicture); Log.v(TAG, "will now release camera"); mCamera.release(); Log.v(TAG, "will now call finish()"); finish(); } }); } private PictureCallback mPicture = new PictureCallback() { @Override public void onPictureTaken(byte[] data, Camera camera) { Log.v(TAG, "Getting output media file"); File pictureFile = getOutputMediaFile(); if (pictureFile == null) { Log.v(TAG, "Error creating output file"); return; } try { FileOutputStream fos = new FileOutputStream(pictureFile); fos.write(data); fos.close(); } catch (FileNotFoundException e) { Log.v(TAG, e.getMessage()); } catch (IOException e) { Log.v(TAG, e.getMessage()); } } }; private static File getOutputMediaFile() { String state = Environment.getExternalStorageState(); if (!state.equals(Environment.MEDIA_MOUNTED)) { return null; } else { File folder_gui = new File(Environment.getExternalStorageDirectory() + File.separator + "GUI"); if (!folder_gui.exists()) { Log.v(TAG, "Creating folder: " + folder_gui.getAbsolutePath()); folder_gui.mkdirs(); } File outFile = new File(folder_gui, "temp.jpg"); Log.v(TAG, "Returnng file: " + outFile.getAbsolutePath()); return outFile; } } After clicking the Button, I get logs: "will now take picture", "will now release camera" and "will now call finish". The activity finishes succesfully, but the Callback function was not called during the mCamera.takePicture(null, null, mPicture); function (There were no logs from the mPicture callback or getMediaOutputFile functions) and there is no file in the location that was specified. Any ideas? :) Much thanks!

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  • Assigning int to byte in java?

    - by user303218
    int val =233; byte b = (byte)val; System.out.println(b); I have a simple case, like one integer with some value & i want to convert that value & place in the byte type for output. But in this case negative value is coming? How to successfully place the int value to byte type.

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  • CPU ordering in Linux (with hyper threading)

    - by Jason
    I'm curious what the CPU ordering is in Linux. Say I bind a thread to cpu0 and another to cpu1 on a hyperthreaded system, are they both going to be on the same physical core. Given a Core i7 920 with 4 cores and hyperthreading, the output of /proc/cpuinfo has me thinking that cpu0 and cpu1 are different physical cores, and cpu0 and cpu4 are on the same physical core. Thanks.

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