You can do it with `paste` function

        &gt; paste(c(&#39;A&#39;, &#39;B&#39;, &#39;C&#39;), collapse=&#39;, &#39; )
        [1] &quot;A, B, C&quot;

You can do it with `str_c` function

    &gt; library(&#39;stringr&#39;)
    &gt; str_c(c(&#39;A&#39;,&#39;B&#39;,&#39;C&#39;),collapse=&#39;,&#39;)    
    [1] &quot;A,B,C&quot;

The shortest method is to use the base toString function. In any case the output string will contain commas

    vector&lt;-c(&#39;A&#39;, &#39;B&#39;, &#39;C&#39;)

    toString(vector)

if you don&#39;t want commas

    gsub(&quot;,&quot;,&quot;&quot;,toString(vector))

If you want any other separator you can substitute anything you like in gsub instead of replacing commas with nothing

Also from `stringr` is the `str_flatten` function: 

```
library(stringr)

str_flatten(c(&quot;A&quot;, &quot;B&quot;, &quot;C&quot;), &quot;,&quot;)
[1] &quot;A,B,C&quot;
```

Can you please help me how to convert the following codes to using &quot;in&quot; operator of criteria builder?
I need to filter by using list/array of usernames using &quot;in&quot;.

*I also tried to search using JPA CriteriaBuilder - &quot;in&quot; method but cannot find good result.
So I would really appreciate also if you can give me reference URLs for this topic. Thanks.*

Here is my codes:

    //usersList is a list of User that I need to put inside IN operator 
    
    CriteriaBuilder builder = getJpaTemplate().getEntityManagerFactory().getCriteriaBuilder();
    CriteriaQuery&lt;ScheduleRequest&gt; criteria = builder.createQuery(ScheduleRequest.class);
    
    Root&lt;ScheduleRequest&gt; scheduleRequest = criteria.from(ScheduleRequest.class);
    criteria = criteria.select(scheduleRequest);
    
    List&lt;Predicate&gt; params = new ArrayList&lt;Predicate&gt;();
    
    List&lt;ParameterExpression&lt;String&gt;&gt; usersIdsParamList = new ArrayList&lt;ParameterExpression&lt;String&gt;&gt;();
    
    for (int i = 0; i &lt; usersList.size(); i++) {
    ParameterExpression&lt;String&gt; usersIdsParam = builder.parameter(String.class);
    params.add(builder.equal(scheduleRequest.get(&quot;createdBy&quot;), usersIdsParam) );
    usersIdsParamList.add(usersIdsParam);
    }
    
    criteria = criteria.where(params.toArray(new Predicate[0]));
    
    TypedQuery&lt;ScheduleRequest&gt; query = getJpaTemplate().getEntityManagerFactory().createEntityManager().createQuery(criteria);
    
    for (int i = 0; i &lt; usersList.size(); i++) {
    query.setParameter(usersIdsParamList.get(i), usersList.get(i).getUsername());
    }
    
    List&lt;ScheduleRequest&gt; scheduleRequestList = query.getResultList();

The internal Query String is converted to below, so I don&#39;t get the records created by the two users, because it is using &quot;AND&quot;.

    select generatedAlias0 from ScheduleRequest as generatedAlias0 where ( generatedAlias0.createdBy=:param0 ) and ( generatedAlias0.createdBy=:param1 ) order by generatedAlias0.trackingId asc 

JPA CriteriaBuilder - How to use &quot;IN&quot; comparison operator

I know what covariance and contravariance of types are. My question is why haven&#39;t I encountered discussion of these concepts yet in my study of Haskell (as opposed to, say, Scala)?

It seems there is a fundamental difference in the way Haskell views types as opposed to Scala or C#, and I&#39;d like to articulate what that difference is.

Or maybe I&#39;m wrong and I just haven&#39;t learned enough Haskell yet :-)


Why aren&#39;t there many discussions about co- and contra-variance in Haskell (as opposed to Scala or C#)?

There is a list which I would like to output into an excel file as a single string.
I start with a list of characters.

      url=&quot;http://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pubmed&amp;id=21558518&amp;retmode=xml&quot;
      xml = xmlTreeParse(url,useInternal = T)
      ns &lt;- getNodeSet(xml, &#39;//PublicationTypeList/PublicationType&#39;)  
      types &lt;- sapply(ns, function(x) { xmlValue(x) } )  
      types

Output is this:

    [1] &quot;Journal Article&quot;                      &quot;Multicenter Study&quot;                    &quot;Research Support, N.I.H., Extramural&quot;
    [4] &quot;Research Support, Non-U.S. Gov&#39;t&quot;    

So in types - there is a list of characters
Now I need to make into a single string.
This is what I have so far but it is not optimal:


 

     types_as_string = as.character(types[[1]])
          if (length(types) &gt; 1) for (j in 2:length(types))   types_as_string = paste(types_as_string,&quot;| &quot;,as.character(types[[j]]),sep=&quot;&quot;)
     types_as_string          
     [1] &quot;Journal Article| Multicenter Study| Research Support, N.I.H., Extramural| Research Support, Non-U.S. Gov&#39;t&quot;

&gt; 


So I want to end up with a nice string separated by pipes or other separator. (the last code part - is what I want to re-write nicely). The pipes are important and they have to be properly done. 

How to collapse a list of characters into a single string in R

There is a list which I would like to output into an excel file as a single string.
I start with a list of characters.
<pre><code class="hljs language-ini"> url="http://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pubmed&#x26;id=21558518&#x26;retmode=xml"
 xml = xmlTreeParse(url,useInternal = T)
 ns &#x3C;- getNodeSet(xml, '//PublicationTypeList/PublicationType') 
 types &#x3C;- sapply(ns, function(x) { xmlValue(x) } ) 
 types
</code></pre>
Output is this:
<pre><code class="hljs language-csharp">[1] "Journal Article" "Multicenter Study" "Research Support, N.I.H., Extramural"
[4] "Research Support, Non-U.S. Gov't" 
</code></pre>
So in types - there is a list of characters
Now I need to make into a single string.
This is what I have so far but it is not optimal:
<pre><code class="hljs language-lua"> types_as_string = as.character(types[[1]])
 if (length(types) > 1) for (j in 2:length(types)) types_as_string = paste(types_as_string,"| ",as.character(types[[j]]),sep="")
 types_as_string 
 [1] "Journal Article| Multicenter Study| Research Support, N.I.H., Extramural| Research Support, Non-U.S. Gov't"
</code></pre>
>
So I want to end up with a nice string separated by pipes or other separator. (the last code part - is what I want to re-write nicely). The pipes are important and they have to be properly done.

I want to know what&#39;s the best way to make the `String.include?` methods ignore case. Currently I&#39;m doing the following. Any suggestions? Thanks!

    a = &quot;abcDE&quot;
    b = &quot;CD&quot;
    result = a.downcase.include? b.downcase

Edit:
How about `Array.include?`. All elements of the array are strings.

Case-insensitive Array#include?

In PHP, I have an array of variables that are ALL strings.  Some of the values stored are numeric strings with commas.  

What I need:

A way to trim the commas from strings, and ONLY do this for numeric strings.  This isn&#39;t as straightforward as it looks.  The main reason is that the following fails:

    $a = &quot;1,435&quot;;
    
    if(is_numeric($a))
        $a = str_replace(&#39;,&#39;, &#39;&#39;, $a);

This fails because `$a = &quot;1435&quot;` is numeric.  But `$a = &quot;1,435&quot;` is not numeric.  Because some of the strings I get will be regular sentences with commas, I can&#39;t run a string replace on every string. 




PHP remove commas from numeric strings

I want to do the following in C# (coming from a Python background):

    strVar = &quot;stack&quot;
    mystr  = &quot;This is %soverflow&quot; % (strVar)

How do I replace the token inside the string with the value outside of it?

How do I interpolate strings?

String does not have `ReplaceAt()`, and I&#39;m tumbling a bit on how to make a decent function that does what I need. I suppose the CPU cost is high, but the string sizes are small so it&#39;s all ok

Replacing a char at a given index in string?

I&#39;m trying to convert some code from Python to C++ in an effort to gain a little bit of speed and sharpen my rusty C++ skills.  Yesterday I was shocked when a naive implementation of reading lines from stdin was much faster in Python than C++ (see [this][1]).  Today, I finally figured out how to split a string in C++ with merging delimiters (similar semantics to python&#39;s split()), and am now experiencing deja vu!  My C++ code takes much longer to do the work (though not an order of magnitude more, as was the case for yesterday&#39;s lesson).

**Python Code:**

    #!/usr/bin/env python
    from __future__ import print_function                                            
    import time
    import sys
    
    count = 0
    start_time = time.time()
    dummy = None
    
    for line in sys.stdin:
        dummy = line.split()
        count += 1
    
    delta_sec = int(time.time() - start_time)
    print(&quot;Python: Saw {0} lines in {1} seconds. &quot;.format(count, delta_sec), end=&#39;&#39;)
    if delta_sec &gt; 0:
        lps = int(count/delta_sec)
        print(&quot;  Crunch Speed: {0}&quot;.format(lps))
    else:
        print(&#39;&#39;)


**C++ Code:**

    #include &lt;iostream&gt;                                                              
    #include &lt;string&gt;
    #include &lt;sstream&gt;
    #include &lt;time.h&gt;
    #include &lt;vector&gt;
    
    using namespace std;
    
    void split1(vector&lt;string&gt; &amp;tokens, const string &amp;str,
            const string &amp;delimiters = &quot; &quot;) {
        // Skip delimiters at beginning
        string::size_type lastPos = str.find_first_not_of(delimiters, 0);
    
        // Find first non-delimiter
        string::size_type pos = str.find_first_of(delimiters, lastPos);
    
        while (string::npos != pos || string::npos != lastPos) {
            // Found a token, add it to the vector
            tokens.push_back(str.substr(lastPos, pos - lastPos));
            // Skip delimiters
            lastPos = str.find_first_not_of(delimiters, pos);
            // Find next non-delimiter
            pos = str.find_first_of(delimiters, lastPos);
        }
    }
    
    void split2(vector&lt;string&gt; &amp;tokens, const string &amp;str, char delim=&#39; &#39;) {
        stringstream ss(str); //convert string to stream
        string item;
        while(getline(ss, item, delim)) {
            tokens.push_back(item); //add token to vector
        }
    }
    
    int main() {
        string input_line;
        vector&lt;string&gt; spline;
        long count = 0;
        int sec, lps;
        time_t start = time(NULL);
    
        cin.sync_with_stdio(false); //disable synchronous IO
    
        while(cin) {
            getline(cin, input_line);
            spline.clear(); //empty the vector for the next line to parse
    
            //I&#39;m trying one of the two implementations, per compilation, obviously:
    //        split1(spline, input_line);  
            split2(spline, input_line);
    
            count++;
        };
    
        count--; //subtract for final over-read
        sec = (int) time(NULL) - start;
        cerr &lt;&lt; &quot;C++   : Saw &quot; &lt;&lt; count &lt;&lt; &quot; lines in &quot; &lt;&lt; sec &lt;&lt; &quot; seconds.&quot; ;
        if (sec &gt; 0) {
            lps = count / sec;
            cerr &lt;&lt; &quot;  Crunch speed: &quot; &lt;&lt; lps &lt;&lt; endl;
        } else
            cerr &lt;&lt; endl;
        return 0;
    
    //compiled with: g++ -Wall -O3 -o split1 split_1.cpp

Note that I tried two different split implementations.  One (split1) uses string methods to search for tokens and is able to merge multiple tokens as well as handle numerous tokens (it comes from [here][2]).  The second (split2) uses getline to read the string as a stream, doesn&#39;t merge delimiters, and only supports a single delimeter character (that one was posted by several StackOverflow users in answers to string splitting questions).

I ran this multiple times in various orders.  My test machine is a Macbook Pro (2011, 8GB, Quad Core), not that it matters much.  I&#39;m testing with a 20M line text file with three space-separated columns that each look similar to this: &quot;foo.bar 127.0.0.1   home.foo.bar&quot;

**Results:**

    $ /usr/bin/time cat test_lines_double | ./split.py
           15.61 real         0.01 user         0.38 sys
    Python: Saw 20000000 lines in 15 seconds.   Crunch Speed: 1333333
    $ /usr/bin/time cat test_lines_double | ./split1
           23.50 real         0.01 user         0.46 sys
    C++   : Saw 20000000 lines in 23 seconds.  Crunch speed: 869565
    $ /usr/bin/time cat test_lines_double | ./split2
           44.69 real         0.02 user         0.62 sys
    C++   : Saw 20000000 lines in 45 seconds.  Crunch speed: 444444


What am I doing wrong?  Is there a better way to do string splitting in C++ that does not rely on external libraries (i.e. no boost), supports merging sequences of delimiters (like python&#39;s split), is thread safe (so no strtok), and whose performance is at least on par with python?

**Edit 1 / Partial Solution?:**

I tried making it a more fair comparison by having python reset the dummy list and append to it each time, as C++ does. This still isn&#39;t exactly what the C++ code is doing, but it&#39;s a bit closer. Basically, the loop is now:

    for line in sys.stdin:
        dummy = []
        dummy += line.split()
        count += 1

The performance of python is now about the same as the split1 C++ implementation. 

    /usr/bin/time cat test_lines_double | ./split5.py
           22.61 real         0.01 user         0.40 sys
    Python: Saw 20000000 lines in 22 seconds.   Crunch Speed: 909090

I still am surprised that, even if Python is so optimized for string processing (as Matt Joiner suggested), that these C++ implementations would not be faster.  If anyone has ideas about how to do this in a more optimal way using C++, please share your code.  (I think my next step will be trying to implement this in pure C, although I&#39;m not going to trade off programmer productivity to re-implement my overall project in C, so this will just be an experiment for string splitting speed.)   

Thanks to all for your help.

**Final Edit/Solution:**

Please see Alf&#39;s accepted answer.  Since python deals with strings strictly by reference and STL strings are often copied, performance is better with vanilla python implementations.  For comparison, I compiled and ran my data through Alf&#39;s code, and here is the performance on the same machine as all the other runs, essentially identical to the naive python implementation (though faster than the python implementation that resets/appends the list, as shown in the above edit):

    $ /usr/bin/time cat test_lines_double | ./split6
           15.09 real         0.01 user         0.45 sys
    C++   : Saw 20000000 lines in 15 seconds.  Crunch speed: 1333333

My only small remaining gripe is regarding the amount of code necessary to get C++ to perform in this case.  

One of the lessons here from this issue and yesterday&#39;s stdin line reading issue (linked above) are that one should always benchmark instead of making naive assumptions about languages&#39; relative &quot;default&quot; performance.  I appreciate the education.   

Thanks again to all for your suggestions!

  [1]: https://stackoverflow.com/questions/9371238/why-is-reading-lines-from-stdin-much-slower-in-c-than-python
  [2]: http://oopweb.com/CPP/Documents/CPPHOWTO/Volume/C++Programming-HOWTO-7.html

Why is splitting a string slower in C++ than Python?

How do I use the new line character in R? 

    myStringVariable &lt;- &quot;Very Nice ! I like&quot;;
    
    myStringVariabel &lt;- paste(myStringVariable, &quot;\n&quot;, sep=&quot;&quot;);

The above code **DOESN&#39;T work**

P.S There&#39;s significant challenges when googling this kind of stuff since the query &quot;R new line character&quot; does seem to confuse google. I really wish R had a different name. 

R - do I need to add explicit new line character with print()?

I have an R script that is shared with several users on different computers. One of its lines contains the `install.packages(&quot;xtable&quot;)` command.

The problem is that every time someone runs the script, R spends a great deal of time apparently reinstalling the package (it actually does take some time, since the real case has vector of several packages).

How can I make first check if the packages are installed and then only run `install.packages()` for the ones that are not?

Check for installed packages before running install.packages()

I&#39;d like to check if some variable is defined in R - without getting an error. How can I do this?

My attempts (not successful):

    &gt; is.na(ooxx)
    Error: object &#39;ooxx&#39; not found
    &gt; is.finite(ooxx)
    Error: object &#39;ooxx&#39; not found

Thanks!

How to check if object (variable) is defined in R?

    a &lt;- c(1, 2, 0, 3, 7)

I am looking for a function to return the index of the smallest value, 3. What is it?

Return index of the smallest value in a vector?

    a&lt;-c(1,2,0,7,5)

Some languages have a picker -function -- choose one random number from `a` -- how in R?

Select random element in a list of R?

How can I concat strings in shell?  Is it just...

    var = &#39;my&#39;;
    var .= &#39;string&#39;;

?

Concat strings in a shell script

A common antipattern in Python is to concatenate a sequence of strings using `+` in a loop. This is bad because the Python interpreter has to create a new string object for each iteration, and it ends up taking quadratic time. (Recent versions of CPython can apparently optimize this in some cases, but other implementations can&#39;t, so programmers are discouraged from relying on this.) `&#39;&#39;.join` is the right way to do this.

However, I&#39;ve heard it said ([including here on Stack Overflow](https://stackoverflow.com/questions/10001301/list-slicing-python/10001401#10001401)) that you should _never, ever_ use `+` for string concatenation, but instead always use `&#39;&#39;.join` or a format string. I don&#39;t understand why this is the case if you&#39;re only concatenating two strings. If my understanding is correct, it shouldn&#39;t take quadratic time, and I think `a + b` is cleaner and more readable than either `&#39;&#39;.join((a, b))` or `&#39;%s%s&#39; % (a, b)`.

Is it good practice to use `+` to concatenate two strings? Or is there a problem I&#39;m not aware of?

Any reason not to use &#39;+&#39; to concatenate two strings?

I am just starting to learn Ruby (first time programming), and have a basic syntactical question with regards to variables, and various ways of writing code. 

Chris Pine&#39;s &quot;Learn to Program&quot; taught me to write a basic program like this...

    num_cars_again= 2
    puts &#39;I own &#39; + num_cars_again.to_s + &#39; cars.&#39;

This is fine, but then I stumbled across the tutorial on ruby.learncodethehardway.com, and was taught to write the same exact program like this...

    num_cars= 2
    puts &quot;I own #{num_cars} cars.&quot;


They both output the same thing, but obviously option 2 is a much shorter way to do it. 

Is there any particular reason why I should use one format over the other?



String concatenation vs. interpolation in Ruby

I&#39;m trying to understand what the best practice is and why for concatenating string literals and variables for different cases. For instance, if I have code like this

    StringBuilder sb = new StringBuilder(&quot;AAAAAAAAAAAAA&quot;)
        .append(B_String).append(&quot;CCCCCCCCCCC&quot;).append(D_String)
        .append(&quot;EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE&quot;)
        .append(&quot;FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF&quot;);

Is this the way to do it? From [this post][1], I noticed that the `+` operator on Strings creates a new instance of StringBuilder, concatenates the operands, and returns a String conversion, which seems like a lot more work than just calling `.append()`; so if that&#39;s true, then that is out of the question. But what about `String.concat()`? Is it proper to use `.append()` for every concatenation? Or just for variables, and literals are okay to append with `.concat()`?

    StringBuilder sb = new StringBuilder(&quot;AAAAAAAAAAAAA&quot;)
        .append(B_String.concat(&quot;CCCCCCCCCCC&quot;)).append(D_String
        .concat(&quot;EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE&quot;)
        .concat(&quot;FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF&quot;));

What are the general rules for best practices and performance for going about these situations? Is my assumption correct on `+` and it should really just not be used?


  [1]: https://stackoverflow.com/questions/47605/java-string-concatenation

Best practices/performance: mixing StringBuilder.append with String.concat

What is the best (idiomatic) way to concatenate Strings in Groovy?

Option 1:

    calculateAccountNumber(bank, branch, checkDigit, account) {
        bank + branch + checkDigit + account
    }


Option 2:

    calculateAccountNumber(bank, branch, checkDigit, account) {
        &quot;$bank$branch$checkDigit$account&quot;
    }

I&#39;ve founded an interesting point about this topic in the old Groovy website: Things you can do but better leave undone.

&gt; As in Java, you can concatenate Strings with the &quot;+&quot; symbol. But Java
&gt; only needs that one of the two items of a &quot;+&quot; expression to be a
&gt; String, no matter if it&#39;s in the first place or in the last one. Java
&gt; will use the toString() method in the non-String object of your &quot;+&quot;
&gt; expression. But in Groovy, you just should be safe the first item of
&gt; your &quot;+&quot; expression implements the plus() method in the right way,
&gt; because Groovy will search and use it. In Groovy GDK, only the Number
&gt; and String/StringBuffer/Character classes have the plus() method
&gt; implemented to concatenate strings. To avoid surprises, always use
&gt; GStrings.


Content Type	Original Author	Original Content on Stackoverflow
Question	userJT	View Question on Stackoverflow
Solution 1 - String	ilya	View Answer on Stackoverflow
Solution 2 - String	Chernoff	View Answer on Stackoverflow
Solution 3 - String	Dimitrios Zacharatos	View Answer on Stackoverflow
Solution 4 - String	LMc	View Answer on Stackoverflow

How to collapse a list of characters into a single string in R

String Problem Overview

String Solutions

Solution 1 - String

Solution 2 - String

Solution 3 - String

Solution 4 - String

Why aren't there many discussions about co- and contra-variance in Haskell (as opposed to Scala or C#)?

JPA CriteriaBuilder - How to use "IN" comparison operator

Attributions