Is there an elegant way (elegant meaning without an iterator or a loop) to print every member of Java's List&lt;Sting&gt; object into a comma-separated string?  E.g., Java's version of Perl's my $allElementsString = join(",", @myStrings);  I checked List interface and didn't find anything promising (my best guess was to use toArray and then Array's toString?)
While working in a Java app, I recently needed to assemble a comma-delimited list of values to pass to another web service without knowing how many elements there would be in advance. The best I could come up with off the top of my head was something like this:  public String appendWithDelimiter( String original, String addition, String delimiter ) {     if ( original.equals( "" ) ) {         return addition;     } else {         return original + delimiter + addition;     } }  String parameterString = ""; if ( condition ) parameterString = appendWithDelimiter( parameterString, "elementName", "," ); if ( anotherCondition ) parameterString = appendWithDelimiter( parameterString, "anotherElementName", "," );   I realize this isn't particularly efficient, since there are strings being created all over the place, but I was going for clarity more than optimization.  In Ruby, I can do something like this instead, which feels much more elegant:  parameterArray = []; parameterArray &lt;&lt; "elementName" if condition; parameterArray &lt;&lt; "anotherElementName" if anotherCondition; parameterString = parameterArray.join(",");   But since Java lacks a join command, I couldn't figure out anything equivalent.  So, what's the best way to do this in Java?
What is the optimal distance function for individuals when attributes are nominal? I do not know which distance function between individuals to use in case of nominal (unordered categorical) attributes. I was reading some textbook and they suggest Simple Matching function but some books suggest that I should change the nominal to binary attributes and use Jaccard Coefficient. However, what if the values of the nominal attribute is not 2? what if there are three or four values in that attribute?  Which distance function should I use for nominal attributes? Novel about a teleportation device and a con artist alien What is the limit of Lovers Leap? cron.hourly sendmail errors even though my scripts do not involve sending mail Proof on showing if F(x,y,z)=0 then product of partial derivatives (evaluated at an assigned coordinate) is -1 The task is as follows:     Given: $$F(x,y,z) = 0$$    Goal:  Show    $\frac{\partial  z}{\partial y}|_x \frac{\partial  y}{\partial x}|_z \frac{\partial x}{\partial z} |_y = -1$   Here is my work so far:  (1) Differentiate with respect to y, I get:  $0 + F_2 + F_3  \frac{\partial z}{\partial y} = 0$  So $ F_3  \frac{\partial z}{\partial y} = - F_2$  (2) Differentiate with respect to x, I get:  $F_1 + F_2 \frac{\partial y}{\partial x}  + 0 = 0$  So $ F_2  \frac{\partial y}{\partial x} = - F_1$  (3) Differentiate with respect to z, I get:  $F_1  \frac{\partial x}{\partial z}    + 0  + F_3 = 0$  So $ F_1  \frac{\partial x}{\partial z} = - F_3$  (4) After some manipulations with the $F_i$, I get to the conclusion that $\frac{\partial z}{\partial y}* \frac{\partial y}{\partial x} * \frac{\partial x}{\partial z}  = -1$, so when evaluated with x, z, y respectively, conclusion is still true  My questions are:  (1) Is my proof correct?  (2) For example, when I differentiate with respect to y, I "let" $F_1$ be 0 and find partials for other coordinates.    I had a hard time trying to explain to my friend on the reason(s) why I can do such "let be 0" thing.  Although I think if I can't do that, then there is no way that I can reach the conclusion, but I somehow feel confused about the fact too.  Since my book is doing it that way, my understanding is that I can do such "let be 0" thing based on the independece of x with respect to y, when I differentiate with respect to y.  But is my thought ok?  Would someone please help me on this question? Thank you very much ^_^ Let $A = \mathbb{Z}$, $B = [−1, \pi]$, $C = (2, 7)$. List all elements of $A \cap (B^c \cap C)$. After working it out on a number line, I got: $\{4, 5, 6\}$.  As it stands, the expression contains the integers that do not belong to the set $B$ that cross into $C$. This would result in $4, 5, 6$. Number $7$ would not be included because of the soft brackets surrounding $C = (2, 7)$. Is this correct? Smileys in LaTeX I would like to include smileys in my LaTeX document. Is there any package with lots of different smileys?  In mnsymbol and wasysym, I found some general symbols:  \documentclass{article} \usepackage{MnSymbol,wasysym} \begin{document} wasysym: \smiley{} \frownie{} \blacksmiley{}  MnSymbol: \(\smile{} \frown{}\) \end{document}     But I do not like the output. Actually, I am looking for smileys which look like "default smiles" in Google Talk, MSN, ... ;) &lt;- this one is my favourite. ;) Matrix doesn't shrink when put in fraction. I am trying to implement  using additive ElGamal.  I am trying to run the full protocol mentioned in Section 3.4 on the following inputs:   $p = 17$ (prime) $g = 6$ (generator) $x = 5$ (private key) $k = g^x \pmod p = 6^5 \pmod{17} = 7$ (public key)   Suppose the clients inputs are 1, 2. Then $P(x) = (x-1)(x-2) = x^2-3x+2$, and therefore the coeffiecients to encrypt are $(1, -3, 2)$. I chose $y = 10$ and so the encrypted values are:   $1$ becomes $(15,12)$ $-3$ becomes $(15, 1)$ $2$  becomes $(15, 4)$.   The Server Side Input Set $S=\{1\}$ and the random value $r0$ corresponding to $\{1\}$ is $r_0=2$.    With the above problem in context, I have some questions:   What does P 0,j refer to in Step 7. Can you please give an example? In Step 8, suddenly variable i is introduced along with j. What does i, j, refer to? In Step 8, ENC() function has a ; in between. How do we interpret ENC(a;b)? This question aims to create an &quot;&quot;  of numerous questions that ask about determinants of specific matrices (I may have missed a few):              The general question of this type is  Let $A$ be a square matrix of rank$~1$, let $I$ the identity matrix of the same size, and $\lambda$ a scalar. What is the determinant of $A+\lambda I$?  A clearly very closely related question is  What is the characteristic polynomial of a matrix $A$ of rank$~1$? MySQL: LEFT JOIN not working as expected Which Stack Exchange site is best for AutoCAD questions? Prove that $\mathbb{Z}$ is not isomorphic to additive group of any vector space over any field.  Proof.  Surpose that: $\phi : (A, +) \rightarrow  \mathbb{Z} $ is an isomorphism. Then there is some $r∈A $ such that $ϕ(r)=1_\mathbb{Z}$. We have $$ 1_\mathbb{Z}=ϕ(r)=ϕ(2(r/2))=2ϕ(r/2)$$  or equivalently that $ϕ(r/2)=\frac{1}{2}$. But this is not in $ \mathbb{Z}$, so there can be no such morphism.  Is my proof above correct? Thanks Is a semigroup with unique right identity and left inverse a group? We know that a semigroup with a right identity and right inverse for all elements is a group (e.g. see ). Symmetrically, also a left identity together with a left inverse implies a group. We also know that a semigroup with a right identity and a left inverse is NOT necessarily a group (see ). My questions are:   in a semigroup, is the existence of a UNIQUE right identity together with the existence of a left inverse enough to have a group? in a semigroup, is the existence of a right identity together with the existence of a UNIQUE left inverse enough to have a group?   I think both these claims are false,  ut haven't found a counter-example so far. Evaluation of $\int_{0}^{1}\frac{x\ln (x)}{\sqrt{1-x^2}}dx$ Evaluation of $\displaystyle \int_{0}^{1}\frac{x\ln (x)}{\sqrt{1-x^2}}dx$   $\bf{My\; Try::}$ Let $\displaystyle I = \int_{0}^{1}\frac{x\ln x}{\sqrt{1-x^2}}dx\;,$ Put $x=\cos \phi\;,$ Then $dx = -\sin \phi d\phi$  and Changing Limit, We get  $$\displaystyle I = -\int_{\frac{\pi}{2}}^{0}\cos \phi \cdot \ln(\cos \phi )d\phi = \int_{0}^{\frac{\pi}{2}} \ln(\cos \phi)\cdot \cos \phi d\phi$$  Now Using Integration by parts, We get  $$\displaystyle I = \left[\ln(\cos \phi)\cdot \sin \phi\right]_{0}^{\frac{\pi}{2}}+\int_{0}^{\frac{\pi}{2}}\frac{\sin^2 \phi}{\cos \phi}d\phi$$  So $$\displaystyle I = \left[\ln(\cos \phi)\cdot \sin \phi\right]_{0}^{\frac{\pi}{2}}+\int_{0}^{\frac{\pi}{2}}\frac{(1-\cos^2 \phi)}{\cos \phi}d\phi$$  So $$\displaystyle I = \left[\ln(\cos \phi)\cdot \sin \phi\right]_{0}^{\frac{\pi}{2}}+\int_{0}^{\frac{\pi}{2}}\sec \phi d\phi-\int_{0}^{\frac{\pi}{2}}\cos \phi d\phi$$  So $$\displaystyle I = \left[\ln(\cos \phi)\cdot \sin \phi\right]_{0}^{\frac{\pi}{2}}+\left[\ln\left|\sec \phi+\tan \phi\right|\right]_{0}^{\frac{\pi}{2}}-\left[\sin \phi\right]_{0}^{\frac{\pi}{2}}$$  So $$\displaystyle I = \left[\ln(\cos \phi)\cdot \sin \phi\right]_{0}^{\frac{\pi}{2}}+\left[\ln\left|\sec \phi+\tan \phi\right|\right]_{0}^{\frac{\pi}{2}}-1$$  Now How can I solve after that, Help Required, Thanks Uniform convergence on two separate intervals What is the best way(s) to fake function overloading in Javascript?   I know it is not possible to overload functions in Javascript as in other languages.  If I needed a function with two uses foo(x) and foo(x,y,z) which is the best / preferred way:   Using different names in the first place Using optional arguments like y = y || 'default' Using number of arguments Checking types of arguments Or how? Can I carry spare Lithium-Ion batteries with me on Lufthansa? I am travelling from the US to India on Lufthansa. I have five spare Lithium-ion batteries, each 850mAh.  Can I bring them back safely? How do I install the latest  on Ubuntu? I've been looking around, and I can't find anything. Is there a Ubuntu package for node.js, or do I have to compile it myself? How to use EntityFieldQuery with dates? I need to select entities with specific dates.   How should the following be formatted. Do I need to parse 15-May-2010  Also how I get the error page.   function events2() {  $query = new EntityFieldQuery(); $query   -&gt;entityCondition('entity_type', 'node', '=')   -&gt;propertyCondition('status', 1, '=')   -&gt;propertyCondition('type', 'event')     -&gt;propertyCondition('field_event_date', '15-May-2010', '=');  $result = $query-&gt;execute();   return $result;  }