    A[A==NDV]=numpy.nan

A==NDV will produce a boolean array that can be used as an index for A

I have a problem. I wrote a big Haskell program, and it always works with small input. Now, when I want to test it and generate a bigger input, I always get the message:

    HsProg: Prelude.head: empty list

I use `Prelude.head` many times. What can I do to find out more or get a better error output to get the code line in which it happens?

How to debug Haskell code?

I&#39;m using a timer to create a stop watch. The timer works by increasing a integer value. I want to then display this value in the activity by constantly updating a textview. 

Here&#39;s my code from the service where I try and update the activity&#39;s textview: 

    protected static void startTimer() {
		isTimerRunning = true; 
		timer.scheduleAtFixedRate(new TimerTask() {
	        public void run() {
	            elapsedTime += 1; //increase every sec
	            StopWatch.time.setText(formatIntoHHMMSS(elapsedTime)); //this is the textview
	        }
	    }, 0, 1000);
	}

I got some kind of error about updating the UI in the wrong thread. 

How can I adapt my code to accomplish this task of constantly updating the textview? 

Android timer updating a textview (UI)

I am looking to replace a number with NaN in numpy and am looking for a function like numpy.nan_to_num, except in reverse.

The number is likely to change as different arrays are processed because each can have a uniquely define NoDataValue.  I have see people using dictionaries, but the arrays are large and filled with both positive and negative floats.  I suspect that it is not efficient to try to load all of these into anything to create keys.

I tried using the following and numpy requiring that I use any() or all().  I realize that I need to iterate element wise, but hope that a built-in function can achieve this.


    def replaceNoData(scanBlock, NDV):
        for n, i in enumerate(array):
            if i == NDV:
                scanBlock[n] = numpy.nan
            
            
        
NDV is GDAL&#39;s no data value and array is a numpy array.

Is a masked array the way to go perhaps?

Numpy - Replace a number with NaN

I am looking to replace a number with NaN in numpy and am looking for a function like numpy.nan_to_num, except in reverse.
The number is likely to change as different arrays are processed because each can have a uniquely define NoDataValue. I have see people using dictionaries, but the arrays are large and filled with both positive and negative floats. I suspect that it is not efficient to try to load all of these into anything to create keys.
I tried using the following and numpy requiring that I use any() or all(). I realize that I need to iterate element wise, but hope that a built-in function can achieve this.
<pre><code class="hljs language-ini">def replaceNoData(scanBlock, NDV):
 for n, i in enumerate(array):
 if i == NDV:
 scanBlock[n] = numpy.nan
 
 
 
</code></pre>
NDV is GDAL's no data value and array is a numpy array.
Is a masked array the way to go perhaps?

Suppose I want to change `the blue dog and blue cat wore blue hats` to `the gray dog and gray cat wore blue hats`.

With `sed` I could accomplish this as follows:

    $ echo &#39;the blue dog and blue cat wore blue hats&#39; | sed &#39;s/blue $dog\|cat$/gray \1/g&#39;

How can I do a similar replacement in Python? I&#39;ve tried:

    &gt;&gt;&gt; import re
    &gt;&gt;&gt; s = &quot;the blue dog and blue cat wore blue hats&quot;
    &gt;&gt;&gt; p = re.compile(r&quot;blue (dog|cat)&quot;)
    &gt;&gt;&gt; p.sub(&#39;gray \1&#39;,s)
    &#39;the gray \x01 and gray \x01 wore blue hats&#39;




How to use python regex to replace using captured group?

I have a set of strings, e.g.

    my_prefix_what_ever
    my_prefix_what_so_ever
    my_prefix_doesnt_matter

I simply want to find the longest common portion of these strings, here the prefix. In the above the result should be

    my_prefix_

The strings

    my_prefix_what_ever
    my_prefix_what_so_ever
    my_doesnt_matter

should result in the prefix

    my_

Is there a relatively painless way in Python to determine the prefix (without having to iterate over each character manually)?

PS: I&#39;m using Python 2.6.3.


Determine prefix from a set of (similar) strings

Is anyone using anything like this in Python:

    def die(error_message):
        raise Exception(error_message)
    
    ...
    
    check_something() or die(&#39;Incorrect data&#39;)

I think this kind of style is used in PHP and Perl.

Do you find any (dis)advantages in this [style]?

&quot;or die()&quot; in Python

I&#39;ve been using `argparse` for a Python program that can `-process`, `-upload` or both:

    parser = argparse.ArgumentParser(description=&#39;Log archiver arguments.&#39;)
    parser.add_argument(&#39;-process&#39;, action=&#39;store_true&#39;)
    parser.add_argument(&#39;-upload&#39;,  action=&#39;store_true&#39;)
    args = parser.parse_args()

The program is meaningless without at least one parameter. How can I configure `argparse` to force at least one parameter to be chosen?

**UPDATE:**

Following the comments: What&#39;s the Pythonic way to parametrize a program with at least one option?

Python argparse: Make at least one argument required

How does python handle generic/template type scenarios?  Say I want to create an external file &quot;BinaryTree.py&quot; and have it handle binary trees, but for any data type.  

So I could pass it the type of a custom object and have a binary tree of that object.  How is this done in python?

Generics/templates in python?

I have String array with some components, this array has 5 components and it vary some times. What I would like to do is to iterate through that array and get the first component and the component next to that one. So the first time I would get the component number one and the component number 2, the second time would get the number 2 and 3, the third time number 3 and 4... And so on until you get to the last component. 

This how far I have come: 


    String[] elements = { &quot;a&quot;, &quot;a&quot;,&quot;a&quot;,&quot;a&quot; };
        
    for( int i = 0; i &lt;= elements.length - 1; i++)
    {
        // get element number 0 and 1 and put it in a variable, 
        // and the next time get element      1 and 2 and put this in another variable. 
    }


How can I accomplish this?




Iterate through string array in Java

If I have this array:

    array(&quot;  hey  &quot;, &quot;bla  &quot;, &quot;  test&quot;);

and I want to trim all of them, How can I do that?

The array after the trim:

    array(&quot;hey&quot;, &quot;bla&quot;, &quot;test&quot;);

How can I trim all strings in an Array?

I&#39;m trying to think of the best way to return an empty array, rather than `null`.

Is there any difference between `foo()` and `bar()`?

    private static File[] foo() {
        return Collections.emptyList().toArray(new File[0]);
    }

&lt;!-- separator --&gt;

    private static File[] bar() {
        return new File[0];
    }

Returning an empty array

I have an array which is multidimensional for no reason

    /* This is how my array is currently */
    Array
    (
    [0] =&gt; Array
        (
            [0] =&gt; Array
                (
                    [plan] =&gt; basic
                )
 
            [1] =&gt; Array
                (
                    [plan] =&gt; small
                )
 
            [2] =&gt; Array
                (
                    [plan] =&gt; novice
                )
 
            [3] =&gt; Array
                (
                    [plan] =&gt; professional
                )
 
            [4] =&gt; Array
                (
                    [plan] =&gt; master
                )
 
            [5] =&gt; Array
                (
                    [plan] =&gt; promo
                )
 
            [6] =&gt; Array
                (
                    [plan] =&gt; newplan
                )
 
        )
 
     )

 
I want to convert this array into this form

    /*Now, I want to simply it down to this*/
    Array (
	[0] =&gt; basic
	[1] =&gt; small
	[2] =&gt; novice
	[3] =&gt; professional
	[4] =&gt; master
	[5] =&gt; promo
	[6] =&gt; newplan
    )

Any idea how to do this? 

Convert multidimensional array into single array

What is a function in PHP used to convert array to string, other than using JSON?

I know there is a function that directly does like JSON. I just don&#39;t remember.

How to convert array to a string using methods other than JSON?

I&#39;m looking for the fastest way to check for the occurrence of NaN (`np.nan`) in a NumPy array `X`. `np.isnan(X)` is out of the question, since it builds a boolean array of shape `X.shape`, which is potentially gigantic.

I tried `np.nan in X`, but that seems not to work because `np.nan != np.nan`. Is there a fast and memory-efficient way to do this at all?

(To those who would ask &quot;how gigantic&quot;: I can&#39;t tell. This is input validation for library code.)

Fast check for NaN in NumPy

Believe it or not, after profiling my current code, the repetitive operation of numpy array reversion ate a giant chunk of the running time. What I have right now is the common view-based method:

    reversed_arr = arr[::-1]

Is there any other way to do it more efficiently, or is it just an illusion from my obsession with unrealistic numpy performance?

Most efficient way to reverse a numpy array

Is there a way to efficiently implement a rolling window for 1D arrays in Numpy?

For example, I have this pure Python code snippet to calculate the rolling standard deviations for a 1D list, where `observations` is the 1D list of values, and `n` is the window length for the standard deviation:

    stdev = []
    for i, data in enumerate(observations[n-1:]):
      	strip = observations[i:i+n]
       	mean = sum(strip) / n
       	stdev.append(sqrt(250*sum([(s-mean)**2 for s in strip])/(n-1)))

Is there a way to do this completely within Numpy, i.e., without any Python loops? The standard deviation is trivial with `numpy.std`, but the rolling window part completely stumps me.

I found [this][1] blog post regarding a rolling window in Numpy, but it doesn&#39;t seem to be for 1D arrays. 


  [1]: http://www.rigtorp.se/2011/01/01/rolling-statistics-numpy.html

Rolling window for 1D arrays in Numpy?

**Is it possible to map a NumPy array in place? If yes, how?**

Given `a_values` - 2D array - this is the bit of code that does the trick for me at the moment:

    for row in range(len(a_values)):
        for col in range(len(a_values[0])):
            a_values[row][col] = dim(a_values[row][col])

But it&#39;s so ugly that I suspect that somewhere within NumPy there must be a function that does the same with something looking like:

    a_values.map_in_place(dim)

but if something like the above exists, I&#39;ve been unable to find it.


Mapping a NumPy array in place

As far as I know the option Log=True in the histogram function only refers to the y-axis.

    P.hist(d,bins=50,log=True,alpha=0.5,color=&#39;b&#39;,histtype=&#39;step&#39;)

I need the bins to be equally spaced in log10. Is there something that can do this?

How to have logarithmic bins in a Python histogram

Is it possible somehow to return 0 instead of `NaN` when parsing values in JavaScript?

In case of the empty string `parseInt` returns `NaN`.

Is it possible to do something like that in JavaScript to check for `NaN`?

    var value = parseInt(tbb) == NaN ? 0 : parseInt(tbb)

Or maybe there is another function or jQuery plugin which may do something similar?

How to turn NaN from parseInt into 0 for an empty string?

    parseFloat(&quot;NaN&quot;)
returns &quot;NaN&quot;, but

    parseFloat(&quot;NaN&quot;) == &quot;NaN&quot;
returns false. Now, that&#39;s probably a good thing that it does return false, but I don&#39;t understand how this is so. Did the JavaScript creators just make this a special case? Because otherwise I can&#39;t understand how this returns false.

Is NaN equal to NaN?

I was just studying OCPJP questions and I found this strange code:

    public static void main(String a[]) {
        System.out.println(Double.NaN==Double.NaN);
    	System.out.println(Double.NaN!=Double.NaN);
    }

When I ran the code, I got:

    false
    true

How is the output `false` when we&#39;re comparing two things that look the same as each other? What does `NaN` mean?

Why does Double.NaN==Double.NaN return false?

I need to compare two numeric values for equality in Javascript. The values may be `NaN` as well.
I&#39;ve come up with this code:

    if (val1 == val2 || isNaN(val1) &amp;&amp; isNaN(val2)) ...

which is working fine, but it looks bloated to me. I would like to make it more concise. Any ideas?

Comparing NaN values for equality in Javascript

Please point out the point that I am missing:  

**openSUSE 11.3**

----------


    xx@linux-y3pi:~/Desktop/R&gt; sudo R CMD INSTALL rgdal_0.7-12.tar.gz 
    root&#39;s password:
    * installing to library ‘/usr/lib64/R/library’
    * installing *source* package ‘rgdal’ ...
    ** package ‘rgdal’ successfully unpacked and MD5 sums checked
    configure: gdal-config: gdal-config
    checking gdal-config usability... ./configure: line 1353: gdal-config: command not found
    no
    Error: gdal-config not found
    The gdal-config script distributed with GDAL could not be found.
    If you have not installed the GDAL libraries, you can
    download the source from  http://www.gdal.org/
    If you have installed the GDAL libraries, then make sure that
    gdal-config is in your path. Try typing gdal-config at a
    shell prompt and see if it runs. If not, use:
     --configure-args=&#39;--with-gdal-config=/usr/local/bin/gdal-config&#39;
    with appropriate values for your installation.
    
    ERROR: configuration failed for package ‘rgdal’
    * removing ‘/usr/lib64/R/library/rgdal’


----------

    xx@linux-y3pi:~/Desktop/R&gt; whereis gdal-config
    gdal-config: /usr/local/bin/gdal-config
    
    xx@linux-y3pi:~/Desktop/R&gt; gdal-config 
    Usage: gdal-config [OPTIONS]
    Options:
     [--prefix[=DIR]]
     [--libs]
     [--dep-libs]
     [--cflags]
     [--datadir]
     [--version]
     [--ogr-enabled]
     [--formats]
     xx@linux-y3pi:~/Desktop/R&gt;


----------


    &gt; sessionInfo()
    R version 2.15.1 (2012-06-22)
    Platform: x86_64-unknown-linux-gnu (64-bit)
    
    locale:
     [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
     [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
     [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
     [7] LC_PAPER=C                 LC_NAME=C                 
     [9] LC_ADDRESS=C               LC_TELEPHONE=C            
    [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       
    
    attached base packages:
    [1] stats     graphics  grDevices utils     datasets  methods   base     
    &gt; 


----------

    xx@linux-y3pi:~/Desktop/R&gt; gdal-config --version
    1.9.0

    xx@linux-y3pi:~/Desktop/R&gt; proj
    Rel. 4.8.0, 6 March 2012
    usage: proj [ -beEfiIlormsStTvVwW [args] ] [ +opts[=arg] ] [ files ]


----------

    linux-y3pi:~ # $PATH
    bash: /home/xx/qtsdk-2010.05/qt/bin/:/home/xx/qtsdk-2010.05/bin:/home/xx/qtsdk-2010.05/qt/bin:/home/xx/qtsdk-2010.05/qt/bin/:/home/xx/qtsdk-2010.05/bin:/usr/lib64/mpi/gcc/openmpi/bin:/home/xx/bin:/usr/local/bin:/usr/bin:/sbin:/usr/sbin:/bin:/usr/bin/X11:/usr/X11R6/bin:/usr/games: No such file or directory



Content Type	Original Author	Original Content on Stackoverflow
Question	Jzl5325	View Question on Stackoverflow
Solution 1 - Python	Paul	View Answer on Stackoverflow

Numpy - Replace a number with NaN

Python Problem Overview

Python Solutions

Solution 1 - Python

Android timer updating a textview (UI)

How to debug Haskell code?

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