Just use `matrix`:

    matrix(vec,nrow = 7,ncol = 7)

One advantage of using `matrix` rather than simply altering the dimension attribute as Gavin points out, is that you can specify whether the matrix is filled by row or column using the `byrow` argument in `matrix`.

A matrix is really just a vector with a `dim` attribute (for the dimensions). So you can add dimensions to `vec` using the `dim()` function and `vec` will then be a matrix:

    vec &lt;- 1:49
    dim(vec) &lt;- c(7, 7)  ## (rows, cols)
    vec
    
    &gt; vec &lt;- 1:49
    &gt; dim(vec) &lt;- c(7, 7)  ## (rows, cols)
    &gt; vec
         [,1] [,2] [,3] [,4] [,5] [,6] [,7]
    [1,]    1    8   15   22   29   36   43
    [2,]    2    9   16   23   30   37   44
    [3,]    3   10   17   24   31   38   45
    [4,]    4   11   18   25   32   39   46
    [5,]    5   12   19   26   33   40   47
    [6,]    6   13   20   27   34   41   48
    [7,]    7   14   21   28   35   42   49

I am trying to write to CSV file but there are blank rows in between. How can I remove the blank rows?

    import csv
    b = open(&#39;test.csv&#39;, &#39;w&#39;)
    a = csv.writer(b)
    data = [[&#39;Me&#39;, &#39;You&#39;],\
            [&#39;293&#39;, &#39;219&#39;],\
            [&#39;54&#39;, &#39;13&#39;]]
    a.writerows(data)
    b.close()


Writing to CSV with Python adds blank lines

I&#39;m trying to select all of the elements that have both `.checked` and `.featured` tags. So basically, what I&#39;m looking for is an &quot;and&quot; selector; I don&#39;t know if there is one or not.

Is there any workaround for cases like this?

CSS &quot;and&quot; selector - Can I select elements that have multiple classes?

I have a vector with 49 numeric values. I want to have a 7x7 numeric matrix instead. 

Is there some sort of convenient automatic conversion statement I can use, or do I have to do 7 separate column assignments of the correct vector subsets to a new matrix? I hope that there is something like the oposite of `c(myMatrix)`, with the option of giving the number of rows and/or columns I want to have, of course. 

How to turn a vector into a matrix in R?

<p>I have a vector with 49 numeric values. I want to have a 7x7 numeric matrix instead.</p>
<p>Is there some sort of convenient automatic conversion statement I can use, or do I have to do 7 separate column assignments of the correct vector subsets to a new matrix? I hope that there is something like the oposite of <code>c(myMatrix)</code>, with the option of giving the number of rows and/or columns I want to have, of course.</p>


I have the following plot like below. It was created with this command:

    library(ggplot2)

    df &lt;- data.frame(cond = factor(rep(c(&quot;A&quot;, &quot;B&quot;), each = 200)), 
                     rating = c(rnorm(200), rnorm(200, mean=.8)))

    ggplot(df, aes(x=rating, fill=cond)) + 
    geom_density(alpha = .3) +
    xlab(&quot;NEW RATING TITLE&quot;) +
    ylab(&quot;NEW DENSITY TITLE&quot;)

Now, I want to modify the *legend title* from **cond** into **NEW LEGEND TITLE**.

So, I just added the following line add the end of the above code:

    +labs(colour=&quot;NEW LEGEND TITLE&quot;)

But it doesn&#39;t work. What&#39;s the right way to do it?

![enter image description here][1]


  [1]: http://i.stack.imgur.com/sqpSU.png

How to change legend title in ggplot

I have a data.table with a character column, and want to select only those rows that contain a substring in it.  Equivalent to SQL `WHERE x LIKE &#39;%substring%&#39;`

E.g.

    &gt; Months = data.table(Name = month.name, Number = 1:12)
    &gt; Months[&quot;mb&quot; %in% Name]
    Empty data.table (0 rows) of 2 cols: Name,Number

How would I select only the rows where Name contains &quot;mb&quot;?

How to select R data.table rows based on substring match (a la SQL like)

What is the correct way to change the levels of a `factor` column in a `data.table`  (note: not data frame) 

      library(data.table)
      mydt &lt;- data.table(id=1:6, value=as.factor(c(&quot;A&quot;, &quot;A&quot;, &quot;B&quot;, &quot;B&quot;, &quot;B&quot;, &quot;C&quot;)), key=&quot;id&quot;)

      mydt[, levels(value)]
      [1] &quot;A&quot; &quot;B&quot; &quot;C&quot;


I am looking for something like: 

    mydt[, levels(value) &lt;- c(&quot;X&quot;, &quot;Y&quot;, &quot;Z&quot;)]

But of course, the above line does not work. 
    
        # Actual               # Expected result
        &gt; mydt                  &gt; mydt
           id value                id value
        1:  1     A             1:  1     X
        2:  2     A             2:  2     X
        3:  3     B             3:  3     Y
        4:  4     B             4:  4     Y
        5:  5     B             5:  5     Y
        6:  6     C             6:  6     Z

How does one change the levels of a factor column in a data.table

I have a  compilation of  4 plots drawn together with `par(mfrow=c(2,2))`. I would like to draw a common title for the 2 above plots and a  common title for the 2 below panels that are centered between the 2 left and right plots. 

Is this possible?

Common main title of a figure panel compiled with par(mfrow)

I have trouble working with formula as with text. What I&#39;m trying to do is to concatenate the formula to the title of the graph. However, when I try to work with the formula as with text, I fail:

    model &lt;- lm(celkem ~ rok + mesic)
    formula(model)
    # celkem ~ rok + mesic

This is fine. Now I want to build string like `&quot;my text celkem ~ rok + mesic&quot;` - this is where the problem comes:

    paste(&quot;my text&quot;, formula(model))
    # [1] &quot;my text ~&quot;           &quot;my text celkem&quot;      &quot;my text rok + mesic&quot;

    paste(&quot;my text&quot;, as.character(formula(model)))
    # [1] &quot;my text ~&quot;           &quot;my text celkem&quot;      &quot;my text rok + mesic&quot;

    paste(&quot;my text&quot;, toString(formula(model)))
    # [1] &quot;my text ~, celkem, rok + mesic&quot;

Now I see there is a `sprint` function in package `gtools`, but I think this is such a basic thing that it deserves a solution within the default environment!!

How to convert R formula to text?

I was wondering what are the differences between the two. I notice that emplace is c++11 addition. So why the addition ?

C++ std::vector emplace vs insert

How can I move some elements from first vector to second, and the elements will remove from the first?  
if I am using `std::move`, the elements not removed from first vector.  
this is the code I wrote:  
  
       move(xSpaces1.begin() + 7, xSpaces1.end(), back_inserter(xSpaces2));

Moving elements from std::vector to another one

I am trying to do a foreach on a vector of attacks, each attack has a **unique ID** say, 1-3.

The class method takes the keyboard input of 1-3.

I am trying to use a foreach to run through my elements in m_attack to see if the number matches, if it does... do something.

The problem I&#39;m seeing is this: 

    a&#39;for each&#39; statement cannot operate on an expression of type &quot;std::vector&lt;Attack

Am I going about this totally wrong, I have C# experience and is kind of what I&#39;m basing this on, any help would be appreciated. 

My code is as follows: 

In header

    vector&lt;Attack&gt; m_attack;
In class


    int Player::useAttack (int input)
    {

	    for each (Attack* attack in m_attack) // Problem part
	    {  
            //Psuedo for following action
	     	if (attack-&gt;m_num == input)
	     	{
                //For the found attack, do it&#39;s damage
	    		attack-&gt;makeDamage();
	     	}
	    }
    }

C++ for each, pulling from vector elements

What are the differences between an array and a vector in C++? An example of the differences might be included libraries, symbolism, abilities, etc.

### Array

&gt; Arrays contain a specific number of elements of a particular type. So that the compiler can reserve the required amount of space when the program is compiled, you must specify the type and number of elements that the array will contain when it is defined. The compiler must be able to determine this value when the program is compiled. Once an array has been defined, you use the identifier for the array along with an index to access specific elements of the array. [...] arrays are zero-indexed; that is, the first element is at index 0. This indexing scheme is indicative of the close relationship in C++ between pointers and arrays and the rules that the language defines for pointer arithmetic.
&gt;
&gt; — C++ Pocket Reference

### Vector

&gt; A vector is a dynamically-sized sequence of objects that provides array-style `operator[]` random access. The member function `push_back` copies its arguments via copy constructor, adds that copy as the last item in the vector and increments its size by one. `pop_back` does the exact opposite, by removing the last element. Inserting or deleting items from the end of a vector takes amortized constant time, and inserting or deleting from any other location takes linear time. These are the basics of vectors. There is a lot more to them. In most cases, a vector should be your first choice over a C-style array. First of all, they are dynamically sized, which means they can grow as needed. You don&#39;t have to do all sorts of research to figure out an optimal static size, as in the case of C arrays; a vector grows as needed, and it can be resized larger or smaller manually if you need to. Second, vectors offer bounds checking with the `at` member function (but not with `operator[]`), so that you can do something if you reference a nonexistent index instead of simply watching your program crash or worse, continuing execution with corrupt data.
&gt;
&gt; — C++ Cookbook


Arrays vs Vectors: Introductory Similarities and Differences

Lately I&#39;ve been asked to write a function that reads the binary file into the `std::vector&lt;BYTE&gt;` where `BYTE` is an `unsigned char`. Quite quickly I came with something like this:

    #include &lt;fstream&gt;
    #include &lt;vector&gt;
    typedef unsigned char BYTE;

    std::vector&lt;BYTE&gt; readFile(const char* filename)
    {
        // open the file:
        std::streampos fileSize;
        std::ifstream file(filename, std::ios::binary);

        // get its size:
        file.seekg(0, std::ios::end);
        fileSize = file.tellg();
        file.seekg(0, std::ios::beg);

        // read the data:
        std::vector&lt;BYTE&gt; fileData(fileSize);
        file.read((char*) &amp;fileData[0], fileSize);
        return fileData;
    }

which seems to be unnecessarily complicated and the explicit cast to `char*` that I was forced to use while calling `file.read` doesn&#39;t make me feel any better about it.  

---
Another option is to use [`std::istreambuf_iterator`](http://www.cplusplus.com/reference/iterator/istreambuf_iterator/):

    std::vector&lt;BYTE&gt; readFile(const char* filename)
    {
        // open the file:
        std::ifstream file(filename, std::ios::binary);

        // read the data:
        return std::vector&lt;BYTE&gt;((std::istreambuf_iterator&lt;char&gt;(file)),
                                  std::istreambuf_iterator&lt;char&gt;());
    }

which is pretty simple and short, but still I have to use the `std::istreambuf_iterator&lt;char&gt;` even when I&#39;m reading into `std::vector&lt;unsigned char&gt;`.

---
The last option that seems to be perfectly straightforward is to use [`std::basic_ifstream&lt;BYTE&gt;`](http://en.cppreference.com/w/cpp/io/basic_ifstream), which kinda expresses it explicitly that *&quot;I want an input file stream and I want to use it to read `BYTE`s&quot;*:

    std::vector&lt;BYTE&gt; readFile(const char* filename)
    {
        // open the file:
        std::basic_ifstream&lt;BYTE&gt; file(filename, std::ios::binary);

        // read the data:
        return std::vector&lt;BYTE&gt;((std::istreambuf_iterator&lt;BYTE&gt;(file)),
                                  std::istreambuf_iterator&lt;BYTE&gt;());
    }

but I&#39;m not sure whether [`basic_ifstream`](http://en.cppreference.com/w/cpp/io/basic_ifstream) is an appropriate choice in this case.

*What is the best way of reading a binary file into the `vector`?* I&#39;d also like to know what&#39;s happening *&quot;behind the scene&quot;* and what are the possible problems I might encounter (apart from stream not being opened properly which might be avoided by simple [`is_open`](http://www.cplusplus.com/reference/fstream/ifstream/is_open/) check).

Is there any good reason why one would prefer to use [`std::istreambuf_iterator`](http://www.cplusplus.com/reference/iterator/istreambuf_iterator/) here?  
(the only advantage that I can see is simplicity)

How to read a binary file into a vector of unsigned chars

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?

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.

Content Type	Original Author	Original Content on Stackoverflow
Question	rumtscho	View Question on Stackoverflow
Solution 1 - R	joran	View Answer on Stackoverflow
Solution 2 - R	Gavin Simpson	View Answer on Stackoverflow

How to turn a vector into a matrix in R?

R Problem Overview

R Solutions

Solution 1 - R

Solution 2 - R

CSS "and" selector - Can I select elements that have multiple classes?

Writing to CSV with Python adds blank lines

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