`shape` is a property of both numpy ndarray&#39;s and matrices.

    A.shape

will return a tuple (m, n), where m is the number of rows, and n is the number of columns.

In fact, the numpy `matrix` object is built on top of the `ndarray` object, one of numpy&#39;s two fundamental objects (along with a universal function object), so it inherits from `ndarray`

`matrix.size` according to [the numpy docs](http://docs.scipy.org/doc/numpy/reference/arrays.ndarray.html#array-methods) returns the `Number of elements in the array.` Hope that helps.

As the title of my post suggests, I would like to know how many digits `var number` has. For example: If `number = 15;` my function should return `2`. Currently, it looks like this:

    function getlength(number) {
      return number.toString().length();
    }

But Safari says it is not working due to a `TypeError`:

    &#39;2&#39; is not a function (evaluating &#39;number.toString().length()&#39;)

As you can see, `&#39;2&#39;` is actually the right solution. But why is it `not a function`?

Get number of digits with JavaScript

Seems like there has been a recent update to Google Chrome that causes blurry text after doing a `transform: scale()`. Specifically I&#39;m doing this:

   


&lt;!-- language: lang-css --&gt;

    @-webkit-keyframes bounceIn {
      0% {
        opacity: 0;
        -webkit-transform: scale(.3);
      }

      50% {
        opacity: 1;
        -webkit-transform: scale(1.05);
      }

      70% {
        -webkit-transform: scale(.9);
      }

      100% {
        -webkit-transform: scale(1);
      }
    }


If you visit http://rourkery.com in Chrome, you should see the problem on the main text area. It didn&#39;t used to do this and it doesn&#39;t seem to effect other webkit browsers (like Safari). There were some other posts about people experiencing a similar issue with 3d transforms, but can&#39;t find anything about 2d transforms like this.

Any ideas would be appreciated, thanks!

Blurry text after using CSS transform: scale(); in Chrome

For a numpy matrix in python

    from numpy import matrix
    A = matrix([[1,2],[3,4]])

How can I find the length of a row (or column) of this matrix? Equivalently, how can I know the number of rows or columns?

So far, the only solution I&#39;ve found is:

    len(A)
    len(A[:,1])
    len(A[1,:])

Which returns 2, 2, and 1, respectively. From this I&#39;ve gathered that `len()` will return the number of rows, so I can always us the transpose, `len(A.T)`, for the number of columns. However, this feels unsatisfying and arbitrary, as when reading the line `len(A)`, it isn&#39;t immediately obvious that this should return the number of rows. It actually works differently than `len([1,2])` would for a 2D python array, as this would return 2.

So, is there a more intuitive way to find the size of a matrix, or is this the best I have?


How do I find the length (or dimensions, size) of a numpy matrix in python?

For a numpy matrix in python
<pre><code class="hljs language-lua">from numpy import matrix
A = matrix([[1,2],[3,4]])
</code></pre>
How can I find the length of a row (or column) of this matrix? Equivalently, how can I know the number of rows or columns?
So far, the only solution I've found is:
<pre><code class="hljs language-scss">len(A)
len(A[:,1])
len(A[1,:])
</code></pre>
Which returns 2, 2, and 1, respectively. From this I've gathered that <code>len()</code> will return the number of rows, so I can always us the transpose, <code>len(A.T)</code>, for the number of columns. However, this feels unsatisfying and arbitrary, as when reading the line <code>len(A)</code>, it isn't immediately obvious that this should return the number of rows. It actually works differently than <code>len([1,2])</code> would for a 2D python array, as this would return 2.
So, is there a more intuitive way to find the size of a matrix, or is this the best I have?

    mylist = [&quot;aa123&quot;, &quot;bb2322&quot;, &quot;aa354&quot;, &quot;cc332&quot;, &quot;ab334&quot;, &quot;333aa&quot;]

I need the index position of all items that contain `&#39;aa&#39;`. I&#39;m having trouble combining `enumerate()` with partial string matching. I&#39;m not even sure if I should be using enumerate. 

I just need to return the index positions: 0,2,5





Find all index position in list based on partial string inside item in list

Check the x axis of the figure below. How can I move the labels a bit to the left so that they align with their respective ticks?

I&#39;m rotating the labels using:

    ax.set_xticks(xlabels_positions)
    ax.set_xticklabels(xlabels, rotation=45)

But, as you can see, the rotation is centered on the middle of the text labels. Which makes it look like they are shifted to the right.

I&#39;ve tried using this instead:

    ax.set_xticklabels(xlabels, rotation=45, rotation_mode=&quot;anchor&quot;)

... but it doesn&#39;t do what I wished for. And ``&quot;anchor&quot;`` seems to be the only value allowed for the ``rotation_mode`` parameter.


![Example][1]


  [1]: http://i.stack.imgur.com/LB7Vx.png

Aligning rotated xticklabels with their respective xticks

I have the following XML which I want to parse using Python&#39;s `ElementTree`:

&lt;!-- language: lang-xml --&gt;

    &lt;rdf:RDF xml:base=&quot;http://dbpedia.org/ontology/&quot;
        xmlns:rdf=&quot;http://www.w3.org/1999/02/22-rdf-syntax-ns#&quot;
        xmlns:owl=&quot;http://www.w3.org/2002/07/owl#&quot;
        xmlns:xsd=&quot;http://www.w3.org/2001/XMLSchema#&quot;
        xmlns:rdfs=&quot;http://www.w3.org/2000/01/rdf-schema#&quot;
        xmlns=&quot;http://dbpedia.org/ontology/&quot;&gt;
    
        &lt;owl:Class rdf:about=&quot;http://dbpedia.org/ontology/BasketballLeague&quot;&gt;
            &lt;rdfs:label xml:lang=&quot;en&quot;&gt;basketball league&lt;/rdfs:label&gt;
            &lt;rdfs:comment xml:lang=&quot;en&quot;&gt;
              a group of sports teams that compete against each other
              in Basketball
            &lt;/rdfs:comment&gt;
        &lt;/owl:Class&gt;

    &lt;/rdf:RDF&gt;

I want to find all `owl:Class` tags and then extract the value of all `rdfs:label` instances inside them. I am using the following code:

&lt;!-- language: lang-py --&gt;

    tree = ET.parse(&quot;filename&quot;)
    root = tree.getroot()
    root.findall(&#39;owl:Class&#39;)

Because of the namespace, I am getting the following error.

&lt;!-- language: lang-py --&gt;

    SyntaxError: prefix &#39;owl&#39; not found in prefix map

I tried reading the document at http://effbot.org/zone/element-namespaces.htm but I am still not able to get this working since the above XML has multiple nested namespaces.

Kindly let me know how to change the code to find all the `owl:Class` tags.

Parsing XML with namespace in Python via &#39;ElementTree&#39;

I have to make a program using Euler&#39;s method for the &quot;ball in a spring&quot; model

  

    from pylab import*
    from math import*
    m=0.1
    Lo=1
    tt=30
    k=200
    t=20
    g=9.81
    dt=0.01
    n=int((ceil(t/dt)))
    km=k/m
    r0=[-5,5*sqrt(3)]
    v0=[-5,5*sqrt(3)]
    a=zeros((n,2))
    r=zeros((n,2))
    v=zeros((n,2))
    t=zeros((n,2))
    r[1,:]=r0
    v[1,:]=v0
    for i in range(n-1):
        rr=dot(r[i,:],r[i,:])**0.5
        a=-g+km*cos(tt)*(rr-L0)*r[i,:]/rr
        v[i+1,:]=v[i,:]+a*dt
        r[i+1,:]=r[i,:]+v[i+1,:]*dt
        t[i+1]=t[i]+dt
        
        #print norm(r[i,:])
    
    plot(r[:,0],r[:,1])
    xlim(-100,100)
    ylim(-100,100)
    xlabel(&#39;x [m]&#39;)
    ylabel(&#39;y [m]&#39;)
    
    show()

 
  
I keep getting this error:

 

    a=-g+km*cos(tt)*(rr-L0)*r[i,:]/rr
    RuntimeWarning: invalid value encountered in divide

I can&#39;t figure it out, what is wrong with the code?


RuntimeWarning: invalid value encountered in divide

I am writing a Python module that includes Cython extensions and uses `LAPACK` (and `BLAS`).  I am open to using either `clapack` or `lapacke`, or some kind of `f2c` or `f2py` solution if necessary.  What is important is that I am able to call `lapack` and `blas` routines from Cython in tight loops without Python call overhead.

I&#39;ve found one example [here][1].  However, that example depends on SAGE.  I want my module to be installable without installing SAGE, since my users are not likely to want or need SAGE for anything else.  My users are likely to have packages like numpy, scipy, pandas, and scikit learn installed, so those would be reasonable dependencies.  What is the best combination of interfaces to use, and what would the minimal setup.py file look like that could fetch the necessary information (from numpy, scipy, etc.) for compilation?


  [1]: http://sage.math.washington.edu/home/wstein/www/home/dagss/cython-notur09/lapack/


**EDIT:**
Here is what I ended up doing.  It works on my macbook, but I have no idea how portable it is.  Surely there&#39;s a better way.

    from distutils.core import setup
    from distutils.extension import Extension
    from Cython.Distutils import build_ext
    import numpy
    from Cython.Build import cythonize
    from numpy.distutils.system_info import get_info
    
    # TODO: This cannot be the right way
    blas_include = get_info(&#39;blas_opt&#39;)[&#39;extra_compile_args&#39;][1][2:]
    includes = [blas_include,numpy.get_include()]
    
    setup(
        cmdclass = {&#39;build_ext&#39;: build_ext},
        ext_modules = cythonize([Extension(&quot;cylapack&quot;, [&quot;cylapack.pyx&quot;],
                                           include_dirs = includes,
                                           libraries=[&#39;blas&#39;,&#39;lapack&#39;])
                       ])
    )
    
This works because, on my macbook, the `clapack.h` header file is in the same directory as `cblas.h`.  I can then do this in my pyx file:

    ctypedef np.int32_t integer

    cdef extern from &quot;cblas.h&quot;:
        double cblas_dnrm2(int N,double *X, int incX)
    cdef extern from &quot;clapack.h&quot;:
        integer dgelsy_(integer *m, integer *n, integer *nrhs, 
        double *a, integer *lda, double *b, integer *ldb, integer *
        jpvt, double *rcond, integer *rank, double *work, integer *
        lwork, integer *info)



Distributing Cython based extensions using LAPACK

I&#39;m having issues appending data to a list which is already in a list format. I have a program which will export results objects during a simulation loop. The data itself is stored as a list of matrices. My idea is to store those lists in a list, and then save this list of lists as an R object for later analysis, however I&#39;m having some issues achieving this correctly. I&#39;ll show what I&#39;ve done with small abstract example just using values instead of the matrix data from my simulation:

Say I&#39;ve run the simulation loop for 3 times.
During the iterations, the results lists need to be collected into the one list of lists that I will save as an R object:

List to contain the other lists and be saved: 
`outlist1 &lt;- list()`

First iteration:
`resultsa &lt;- list(1,2,3,4,5)`

`outlist &lt;- append(outlist1,resultsa)`

Second Iteration:
`resultsb &lt;- list(6,7,8,9,10)`

`outlist &lt;- append(outlist1,b)`

Third Iteration:
`resultsc &lt;- list(11,12,13,14,15)`

`outlist &lt;- list(outlist2,c)`


However, this solution does not work with growing a list containing lists this way, the desired result is:

    &gt;outlist
    [[1]]
    [[1]][[1]]
    [1] 1
    
    [[1]][[2]]
    [1] 2
    
    [[1]][[3]]
    [1] 3
    
    [[1]][[4]]
    [1] 4
    
    [[1]][[5]]
    [1] 5
    
    
    [[2]]
    [[2]][[1]]
    [1] 6
    
    [[2]][[2]]
    [1] 7
    
    [[2]][[3]]
    [1] 8
    
    [[2]][[4]]
    [1] 9
    
    [[2]][[5]]
    [1] 10
    
    
    [[3]]
    [[3]][[1]]
    [1] 11
    
    [[3]][[2]]
    [1] 12
    
    [[3]][[3]]
    [1] 13
    
    [[3]][[4]]
    [1] 14
    
    [[3]][[5]]
    [1] 15

However, instead what I get is:

    &gt; outlist3
    [[1]]
    [[1]][[1]]
    [[1]][[1]][[1]]
    [1] 1
    
    [[1]][[1]][[2]]
    [1] 2
    
    [[1]][[1]][[3]]
    [1] 3
    
    [[1]][[1]][[4]]
    [1] 4
    
    [[1]][[1]][[5]]
    [1] 5
    
    
    [[1]][[2]]
    [[1]][[2]][[1]]
    [1] 6
    
    [[1]][[2]][[2]]
    [1] 7
    
    [[1]][[2]][[3]]
    [1] 8
    
    [[1]][[2]][[4]]
    [1] 9
    
    [[1]][[2]][[5]]
    [1] 10

How do I grow a list, such that the resulting list formatted is like the desired result? If I do further analysis on these list I need to be able to easily access the elements.



Appending a list to a list of lists in R

When working with R I frequently get the error message &quot;subscript out of bounds&quot;. [For example][1]:

    # Load necessary libraries and data
    library(igraph)
    library(NetData)
    data(kracknets, package = &quot;NetData&quot;)

    # Reduce dataset to nonzero edges
    krack_full_nonzero_edges &lt;- subset(krack_full_data_frame, (advice_tie &gt; 0 | friendship_tie &gt; 0 | reports_to_tie &gt; 0))

    # convert to graph data farme 
    krack_full &lt;- graph.data.frame(krack_full_nonzero_edges) 
 
    # Set vertex attributes
    for (i in V(krack_full)) {
        for (j in names(attributes)) {
            krack_full &lt;- set.vertex.attribute(krack_full, j, index=i, attributes[i+1,j])
        }
    }

    # Calculate reachability for each vertix
    reachability &lt;- function(g, m) {
        reach_mat = matrix(nrow = vcount(g), 
                           ncol = vcount(g))
        for (i in 1:vcount(g)) {
            reach_mat[i,] = 0
            this_node_reach &lt;- subcomponent(g, (i - 1), mode = m)
 
            for (j in 1:(length(this_node_reach))) {
                alter = this_node_reach[j] + 1
                reach_mat[i, alter] = 1
            }
        }
        return(reach_mat)
    }
 
    reach_full_in &lt;- reachability(krack_full, &#39;in&#39;)
    reach_full_in

This generates the following error `Error in reach_mat[i, alter] = 1 : subscript out of bounds`.

However, my question is not about this particular piece of code (even though it would be helpful to solve that too), but my question is more general:

* What is the definition of a subscript-out-of-bounds error? What causes it?
* Are there any generic ways of approaching this kind of error?


  [1]: http://sna.stanford.edu/sna_R_labs/lab_2.R

Subscript out of bounds - general definition and solution?

I have an `n x m` matrix consisting of non-negative integers. For example:

    2 3 4 7 1
    1 5 2 6 2
    4 3 4 2 1
    2 1 2 4 1
    3 1 3 4 1
    2 1 4 3 2
    6 9 1 6 4

&quot;Dropping a bomb&quot; decreases by one the number of the target cell and all eight of its neighbours, to a minimum of zero.

    x x x 
    x X x
    x x x
What is an algorithm that would determine the minimum number of bombs required to reduce all the cells to zero?

**B Option (Due to me not being a careful reader)**

Actually the first version of problem is not the one I&#39;m seeking answer for. I didn&#39;t carefully read whole task, there&#39;s additional constraints, let us say:

What about simple problem, when sequence in row must be non-increasing:

`8 7 6 6 5` is possible input sequence

`7 8 5 5 2` is not possible since 7 -&gt; 8 growing in a sequence.

Maybe finding answer for &quot;easier&quot; case would help in finding solution for harder one.

**PS:** I believe that when we have several same situations require minimum bombs to clear upper line, we choose one that use most bombs on &quot;left side&quot; of the row. Still any proof that might be correct?

Bomb dropping algorithm

I am looking to sort the following array based on the values of [][0]

    double[][] myArr = new double[mySize][2];

so for example, myArr contents is:
    
    1      5
    13     1.55
    12     100.6
    12.1   .85


I want it to get to:

    1      5
    12     100.6
    12.1   .85
    13     1.55


I am looking to do this without having to implement my own sort.

java Arrays.sort 2d array

How to get a data frame with the same data as an already existing matrix has?

A simplified example of my matrix:

    mat &lt;- matrix(c(0, 0.5, 1, 0.1, 0.2, 0.3, 0.3, 0.4, 0.5),
                  ncol = 3, nrow = 3,
                  dimnames = list(NULL, c(&quot;time&quot;, &quot;C_0&quot;, &quot;C_1&quot;)))

    &gt; mat
         time C_0 C_1
    [1,]  0.0 0.1 0.3
    [2,]  0.5 0.2 0.4
    [3,]  1.0 0.3 0.5

I would like to create a data frame that looks like this:

         name   time   val
    1    C_0    0.0    0.1
    2    C_0    0.5    0.2
    3    C_0    1.0    0.3
    4    C_1    0.0    0.3
    5    C_1    0.5    0.4
    6    C_1    1.0    0.5

All my attempts are quite clumsy, for example:

    data.frame(cbind(c(rep(&quot;C_1&quot;, 3), rep(&quot;C_2&quot;, 3)),
                     rbind(cbind(mat[,&quot;time&quot;], mat[,&quot;C_0&quot;]),
                           cbind(mat[,&quot;time&quot;], mat[,&quot;C_1&quot;]))))

Does anyone have an idea of how to do this more elegantly? Please note that my real data has a few more columns (40 columns).

Create dataframe from a matrix

How to get time difference in seconds from numpy.timedelta64 variable?

    time1 = &#39;2012-10-05 04:45:18&#39;
    time2 = &#39;2012-10-05 04:44:13&#39;
    dt = np.datetime64(time1) - np.datetime64(time2)
    print dt
    
    0:01:05

I&#39;d like to convert `dt` to number (int or float) representing time difference in seconds.

Time difference in seconds from numpy.timedelta64

My question is simple: I have a python script that generates figures using matplotlib. Every time i run it it generates new windows with figures. How can I have the script close windows that were opened the previous time it ran?

the analogous command in matlab is to put &#39;close all&#39; at the beginning of your matlab script.

I have seen several suggestions to do something like

    import matplotlib.pyplot as plt
    plt.close(&quot;all&quot;)

This solution works if you run your script from the python shell, eg using

    &gt;&gt;&gt;&gt; execfile(&quot;myScript.py&quot;)

However, I have found that this doesn&#39;t work if I run the script using Eclipse / PyDev. How can I get it to work in Eclipse?



example:

    from numpy import *
    from matplotlib.pyplot import *
    from scipy import *

    close(&quot;all&quot;) 
        #close any previously open plots - this doesn&#39;t work when running via Eclipse

    t = linspace(0, 0.1,1000)
    w = 60*2*pi

    figure()
    plot(t,cos(w*t))
    plot(t,cos(w*t-2*pi/3))
    plot(t,cos(w*t-4*pi/3))
    show()

This should plot the ideal waveforms for a nice 3-phase power supply.

Close pre-existing figures in matplotlib when running from eclipse

I have sample data which I would like to compute a confidence interval for, assuming a normal distribution.

I have found and installed the numpy and scipy packages and have gotten numpy to return a mean and standard deviation (numpy.mean(data) with data being a list). Any advice on getting a sample confidence interval would be much appreciated.

Compute a confidence interval from sample data

I am trying to do something that is probable very simple. I  would like to save three arrays to a file as columns using &#39;np.savetxt&#39; When I try this

    x = [1,2,3,4]
    y = [5,6,7,8]
    z = [9,10,11,12]

    np.savetxt(&#39;myfile.txt&#39;, (x,y,z), fmt=&#39;%.18g&#39;, delimiter=&#39; &#39;, newline=os.linesep)


The arrays are saved like this

    1 2 3 4
    5 6 7 8
    9 10 11 12

But what I wold like is this 

    1 5 9
    2 6 10
    3 7 11
    4 8 12

 

Content Type	Original Author	Original Content on Stackoverflow
Question	Kyle Heuton	View Question on Stackoverflow
Solution 1 - Python	Kyle Heuton	View Answer on Stackoverflow
Solution 2 - Python	hd1	View Answer on Stackoverflow

How do I find the length (or dimensions, size) of a numpy matrix in python?

Python Problem Overview

Python Solutions

Solution 1 - Python

Solution 2 - Python

Blurry text after using CSS transform: scale(); in Chrome

Get number of digits with JavaScript

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