I am planning to use a $10$-fold strategy in order to validate the results of a logistic regression analysis.  I am a bit confused about the procedure I must follow.  More precisely: Let us suppose that my cross-validation returns acceptable values (for the average AUC, average misclassification rates, etc.) and reveals that everything is OK. Which is the predictive model or formula I should return in such a case?  First of all, I have already read (here, for instance: ) and understood that a $k$-fold cross-validation procedure aims at assessing the performance of a predictive analysis on a given data set (in terms of its ability to accurately predict on new data). I mean, it is not a technique for building predictive models, but a way to measure whether a given fitted model can be overfitting or not (roughly speaking).  OK, so, as far as I understand, I must do this:   Randomly divide the sample into $k$ equally sized subsamples (using stratification if necessary). For $i=1$ to $k$:   Perform a logistic regression analysis using all the cases not in subsample $i$ as the training set. Use subsample $i$ as the validation set. Calculate performance parameters.  Calculate average performance parameters.   Let us imagine that step 3 allows us to conclude that logistic regression performs well on our data.  Now, I have obtained $k$ predictive models. Is this right?  So, which one of them is the final model I should use? Or, should I build (and return to the final user) a definitive logistic regression predictive model using all cases in the sample?  Sorry if this is too simple or too wrong. I would really appreciate if you can answer my questions.  EDIT:  Actually, my question is about cross-validation, but I wanted to specify that I am dealing with logistic regression, just in case it helps.
When performing k-fold cross validation, I understand that you obtain the accuracy metrics by pointing all the folds except one at that one fold and make predictions, and then repeat this process $k$ times.  You can then run accuracy metrics on all of your instances (precision, recall, % classified correctly), which ought to be the same as if you calculated them each time and then averaged the result (correct me if I'm wrong).  The end result you want is a final model.  Do you average the models obtained to make your set of $k$ predictions to end up with the model that has the accuracy metrics obtained by the above method?
Are the hoses in toilets in Asia something I should know about? I have noticed random bits of hose without proper fittings before I think for example in India and just assumed they are for use by the cleaners or for filling the water jug in .  But Now I'm travelling in Malaysia and Singapore and there are more western toilets than squat toilets in the places I've been yet proper hoses with proper fittings are very common in toilets:  (Hose next to a Western style toilet in my hostel in Chinatown, Kuala Lumpur.)  At one place in Singapore there were even signs on each cubicle door stating whether it contained a western or squat toilet, but also whether there was a hose! (I didn't take a photo of the sign, unfortunately)  This makes me think there is a use for the hose for clients, not just cleaners. But for what purpose? Should I know how to use it as a tourist? Please tell me it's not a kind of alternative to a bidet!  Possibly related is the fact that many toilet floors are awash with water. This can be a big problem if you're not wearing waterproof shoes or have to lower your trousers and keep them dry. Other than this toilets are pretty clean and I've seen both the hoses and the wetness in what I would regard as somewhat "fancy" places. Is it possible to take screenshots on the 3DS? In Pokemon X and Y there are specific locations in the game that allows you to save what are essentially 3D screenshots from the upper screen using a virtual camera. This made me wonder - is it possible to take screenshots, 3D or otherwise, from within the 3DS? I was asked this question in an interview.  Lets say we have a correlation matrix of the form \begin{bmatrix}1&amp;0.6&amp;0.8\\0.6&amp;1&amp;\gamma\\0.8&amp;\gamma&amp;1\end{bmatrix}  I was asked to find the value of gamma, given this correlation matrix. I thought I could do something with the eigenvalues, since they should be all greater than or equal to 0.(Matrix should be positive semidefinite) - but I don't think this approach will yield the answer. I am missing a trick.  Could you please provide a hint to solve for the same? Disable three-letter pings from chat to save Oliver, Olivier and Olive from Oli's pings Stop iPhone alerting me when I'm in a phone call When I'm in a phone call, I still get alerts for emails and texts. The noise will play and, if the phone is on Speaker, it will vibrate -- often leading the person I'm talking to wonder what that weird noise was.  Surely there must be a way to silence the phone while you're talking on it. It's very distracting to have beepings going off right next to your ear! Cycles not rendering image or movie clip used as background in the viewport Is it possible to animate which characters of a text object are assigned to a material? I have a table tabName with the following rows:  id(PK) .. Created(datetime)     Resolved(datetime) Status(new/resolved/open) 1          2015-05-10 00:00:00   1970-01-01 ..       open 2          2015-05-10 ..         1970-01-01 ..       new 3          2015-05-10            2015-05-12          resolved 4          2015-05-11 ..         1970-01-01 ..       open 5          2015-05-11 ..         1970-01-01 ..       new 6          2015-05-11            2015-05-11          resolved 7          2015-05-12 ..         1970-01-01 ..       open 8          2015-05-12 ..         1970-01-01 ..       new 9          2015-05-12            2015-05-12          resolved   NOTE:  1970-01-01 .. is default time for all the tickets which are still open.  I have to frame a query to get the count of tickets still open, date wise. Say like on 10 May I have 3 tickets opened. Noting that for id = 3, resolved date is not 10 but it's closed on 12 May.  I framed a query like  SELECT DATE_FORMAT(Created, '%d-%m') AS createdd, COUNT(1) FROM tabName WHERE DATE_FORMAT(Resolved, '%d-%m') &gt; DATE_FORMAT(Created, '%d-%m')       AND YEAR(Created) = '2015' GROUP BY createdd;   The above query gets all the tickets whose Resolved date is greater than the date which is considered for the count. This may count newer tickets as well. And also if the older tickets which are not resolved yet is not counted.  Is there any other way to frame the required query? I have been juggling with this query from last 3 days. Not able to find out still.  Updated: As suggested by Abhik, i have tried in sqlfiddle site.  Here is what i created:  CREATE TABLE test    (idint,createddatetime,resolveddatetime, status varchar(15), PRIMARY KEY (id));    INSERT INTO test       (id,'created','resolved',status`) VALUES       (1,'2015-05-10 00:00:00','1970-01-01 00:00:00','open'),    (2,'2015-05-10 00:00:00','1970-01-01 00:00:00','new'),    (3,'2015-05-10 00:00:00','2015-05-12 00:00:00','resolved'),    (4,'2015-05-11 00:00:00','1970-01-01 00:00:00','open'),    (5,'2015-05-11 00:00:00','1970-01-01 00:00:00','new'),    (6,'2015-05-11 00:00:00','2015-05-11 00:00:00','resolved'),    (7,'2015-05-12 00:00:00','1970-01-01 00:00:00','open'),    (8,'2015-05-12 00:00:00','1970-01-01 00:00:00','new'),    (9,'2015-05-12 00:00:00','1970-01-01 00:00:00','open')    ;   `   When i run  ` select created_date, @open:= @open+open_ticket-resolved as open from(  select   date_format(created,'%d-%m') as created_date ,  sum( case when status='open' then 1 else 0 end )+  sum( case when status='new' then 1 else 0 end )+  sum( case when status='resolved' and ( date(resolved) > date(created) or  date(resolved) = date(created)) then 1 else 0 end ) as open_ticket,  sum(case when status = 'resolved' and date(resolved) = date(created) then 1   else 0 end) as resolved  from test  where  YEAR(Created) = '2015'  group by created_date )x,  (select @open:=0)r order by created_date ; `  I got following output  created_date   open 10-05   3 11-05   5 12-05   8  Here count of still open tickets for 12-05 must be 7. The above query includes ticket id "3" , which is closed on 12-05. So is there any way to exclude this? If i am able to get this right, then i will have full fledged query. Is there a general way to change the font of a particular symbol without switching packages?  For example, suppose I'm using Computer Modern for my entire document, but I want the "subset" operator to look as it does in mathabx.  How can I redefine it to appear in this way? Unable to understand the syntax of the command find The find command seems to differ from other Unix commands.  Why is there the empty curly brackets and a backward flash at the end of the following command?  find * -perm 777 -exec chmod 770 {} \;   I found one reason for the curly brackets but not for the backward flash.   The curly brackets are apparently for the path     Same as -exec, except that ``{}'' is   replaced with as many pathnames as   possible for each invocation of   utility How to view CD key for a Steam game? I have purchased a game on Steam and can not find out the details of the file or purchase. How does one find their CD Key from a game purchased in Steam? I unlocked the 'Files' button/icon from my unity launcher and now it disappearead and I cannot restore it or get it back I unlocked the 'Files' button for the Ubuntu file manager from the unity launcher and I cannot get it back.   When I run the file manager from the dash, the icon does not appear on the launcher like it does for all other applications while they are running. I wanted to have an empty launcher when no applications are running, and just have the icons of those I am actively using there.  Any idea why I don't see it in the launcher when its running or how to lock it back? How can super massive black holes have a lower density than water? I heard on a podcast recently that the  at the centre of some galaxies could have densities less than water, so in theory, they could float on the substance they were gobbling up... can someone explain how something with such mass could float?  Please see the below link for the podcast in question: Is there a string math evaluator in .NET? If I have a string with a valid math expression such as:  String s = "1 + 2 * 7";   Is there a built in library/function in .NET that will parse and evaluate that expression for me and return the result? In this case 15. Is there a bijection of the natural numbers which swaps $\frac{1}{n}$-summable subsets with $\frac{1}{\sqrt{n}}$-summable subsets? Let me start with a precise statement of the question.  For a subset $A\subseteq \mathbb{N}$ and a series of positive real numbers $\sum_{n=0}^\infty a_n$, I'll use the notation $\sum_A a_n$ as a shorthand for $\sum_{n\in A} a_n$.  Is there a bijection $f:\mathbb{N}\rightarrow \mathbb{N}$ with the property that for every $A\subseteq \mathbb{N}$, $\sum_A \frac{1}{n}$ converges iff $\sum_{f(A)} \frac{1}{\sqrt{n}}$ converges?  Background: Fix a series of positive terms $\sum_{n=0}^\infty a_n$.  Given a subset $A\subseteq \mathbb{N}$, call it $a_n$-small if $\sum_A a_n$ converges.  The following proposition is easy to prove:  Proposition:  The set $\{A\subseteq \mathbb{N}: A\text{ is } a_n\text{-small}\}\cup \{\mathbb{N}\}$ is a topology of closed sets on $\mathbb{N}$.  I will use the notation $(\mathbb{N},a_n)$ to refer to this topology.  Then one can ask how topological properties of $(\mathbb{N},a_n)$ are related to series properties of $\sum a_n$.  For example, I can show:  Proposition:  The following are equivalent.  $\sum a_n$ converges.  $(\mathbb{N},a_n)$ is discrete.  $(\mathbb{N},a_n)$ is disconnected.  $(\mathbb{N},a_n)$ is Hausdorff    And there are other nice things.  For example, $(\mathbb{N},a_n)$ is compact iff $(\mathbb{N},a_n)$ is cofinite iff $\liminf a_n &gt; 0$. With this language, my question can be reformulated as...  Are $\left(\mathbb{N}, \frac{1}{n}\right)$ and $\left(\mathbb{N}, \frac{1}{\sqrt{n}}\right)$ homeomorphic?  I have made very little progress on this.  Of course, the identity function $i:(\mathbb{N}, \frac{1}{\sqrt{n}})\rightarrow (\mathbb{N}, \frac{1}{n})$ is a continuous bijection, but the inverse map is not continuous.  Also, if there is such a bijection, there there is such a bijection with agrees with $i$ on any preassigned finite set. Edit  I thought I add in a slightly suprising (to me, at least) example when things work out to be homeomorphic. Begin with a convergent series $\sum c_n$. and divergent series $\sum a_n$ with $\lim a_n = 0$.  Create a new series $b_n$ using all the terms of $c_n$ and $a_n$ (in whatever order you wish).  Then $(\mathbb{N}, a_n)$ and $(\mathbb{N}, b_n)$ are homeomorphic.  The idea is that since $\lim a_n = 0$, there is a convergent infinite subseries $\sum_A a_n$.  Then we use a bijection which with $A$ and $A\cup \{\text{indices of }c_n\}$ to &quot;squeeze&quot; the $c_n$ in without changing the topology.  Of course, I am glossing over many details, but I can include them if desired. Why do we need to set swap space as twice big as our physical memory? When we want to setup a linux system, there is a common a suggestion to set the swap space  twice as big as your physical memory. I want to know why do we need this, and how it is this suggestion come to be? How do I show that $x$ is a root of $p(x)$ in $F[x]/\langle p(x)\rangle$? Let $F$ be a field, and $p(x)$ an irreducible polynomial in $F[X]$. Define $K=F[X]/\langle p(x)\rangle$. For every $a\in F$, denote $\bar{a}=\left&lt;p(x)\right&gt;+a$. How do I show that $\bar{x}\in K$ is a root of $p(x)$?. Connecting subplots Is there a way to draw a sort of connection between subplots in TiKz/pgfplot, like in this ? I'm looking to achieve something like this:    But I would need to draw the "x 2000" line between the plots.  EDIT: So right now I have something like this:    Coming from my main.tex:  \input{aipcheck}  \documentclass[final]{aipproc}  \layoutstyle{8x11single} \usepackage[utf8]{inputenc} \usepackage{algorithm2e} \usepackage{color} \usepackage[usenames,dvipsnames]{xcolor} \usepackage{cleveref} \usepackage{pgfplots}  \pgfplotsset{ tick label style={font=\tiny}, %axis numbers label style={font=\small}, %axis labels legend style={font=\tiny} }  \begin{document}  (...)  \begin{figure}     \centering     \newlength\figureheight      \newlength\figurewidth      \setlength\figureheight{5cm}      \setlength\figurewidth{5cm}     \input{figs/_ddmp2d.tikz} \label{fig2D} \end{figure}   with _ddmp2d.tikz, originally created from matlab2tikz, but already modified, containing:  % This file was created by matlab2tikz v0.3.3. % Copyright (c) 2008--2013, Nico Schlömer &lt;nico.schloemer@gmail.com&gt; % All rights reserved. %  % The latest updates can be retrieved from %   http://www.mathworks.com/matlabcentral/fileexchange/22022-matlab2tikz % where you can also make suggestions and rate matlab2tikz. %  %  %   \begin{tikzpicture}  \begin{axis}[% width=\figurewidth, height=\figureheight, scale only axis, xmin=0, xmax=15, xlabel={Number of iterations}, ymin=0, ymax=16000000000000, name=plot1, after end axis/.append code={\coordinate (a) at (axis description cs:1,0);}]  \addplot [ thick, color=red, dash pattern=on 1pt off 3pt on 3pt off 3pt, forget plot ] table[row sep=crcr]{ 1 15841000000000\\ (...) 15 25160000000\\ }; \addplot [ thick, color=black, dashed, forget plot ] table[row sep=crcr]{ 1 15841000000000\\ (...) 15 52501000000\\ }; \addplot [ thick, color=blue, dotted, forget plot ] table[row sep=crcr]{ 1 15841000000000\\ (...) 15 5324200000\\ }; \addplot [ thick, color=green, solid, forget plot ] table[row sep=crcr]{ 1 15841000000000\\ (...) 15 551920000\\ }; \addplot [ thick, color=green, solid, forget plot ] table[row sep=crcr]{ 3 0\\ 3 16000000000000\\ };  \addplot [ thick, color=blue, dotted, forget plot ] table[row sep=crcr]{ 4 0\\ 4 16000000000000\\ }; \addplot [ thick, color=black, dashed, forget plot ] table[row sep=crcr]{ 5 0\\ 5 16000000000000\\ }; \addplot [ thick, color=red, dash pattern=on 1pt off 3pt on 3pt off 3pt, forget plot ] table[row sep=crcr]{ 8 0\\ 8 16000000000000\\ }; \end{axis}  \begin{scope}[xshift=5cm] \begin{axis}[% width=0.35\figurewidth, height=\figureheight, scale only axis, xmin=995, xmax=1000, xtick={997,998,999,1000}, xticklabels={$997$,$998$,$999$,$1000$}, ymin=0, ymax=8000000000, at=(plot1.right of south east), anchor=left of south west, yticklabel pos=right, axis x discontinuity=crunch, after end axis/.append code={\coordinate (b) at (axis description cs:0,1);} ] \addplot [ thick, color=red, dash pattern=on 1pt off 3pt on 3pt off 3pt ] table[row sep=crcr]{ 995 6093100000\\ 996 6093100000\\ 997 6093100000\\ 998 6093100000\\ 999 6093100000\\ 1000 6093100000\\ };  \addplot [ thick, color=black, dashed ] table[row sep=crcr]{ 995 1577100000\\ 996 1598000000\\ 997 1598500000\\ 998 1628600000\\ 999 1631000000\\ 1000 1595900000\\ };  \addplot [ thick, color=blue, dotted ] table[row sep=crcr]{ 995 2592000000\\ 996 2591900000\\ 997 2591700000\\ 998 2591600000\\ 999 2591500000\\ 1000 2591400000\\ };  \addplot [ thick, color=green, solid ] table[row sep=crcr]{ 995 391810000\\ 996 391810000\\ 997 391810000\\ 998 391810000\\ 999 391810000\\ 1000 391810000\\ };  \end{axis} \draw[gray] (a) -- (b) node[pos=0.5,sloped,fill=white] {$\times$2000}; \end{scope}  \end{tikzpicture}% I want to write an application that detects when a page is loaded in the browser, then I should be able to insert content on top of the loaded web page? Anybody with an idea on how to do that?  Please note that I should be able to do this in any browser (Firefox/IE).  What language should I use to help me do this?  How do I detect this from an external application?  How should I integrate this with the browser? How can I list the contents of a .zip folder in c#? How can I list the contents of a zipped folder in C#? For example how to know how many items are contained within a zipped folder, and what is their name?