How to import data from excel sheet in iOS programmatically
Read data from Excel file in Objective-C (iPhone)
Bottom to top explanation of the Mahalanobis distance? I'm studying pattern recognition and statistics and almost every book I open on the subject I bump into the concept of Mahalanobis distance. The books give sort of intuitive explanations, but still not good enough ones for me to actually really understand what is going on. If someone would ask me "What is the Mahalanobis distance?" I could only answer: "It's this nice thing, which measures distance of some kind" :)   The definitions usually also contain eigenvectors and eigenvalues, which I have a little trouble connecting to the Mahalanobis distance. I understand the definition of eigenvectors and eigenvalues, but how are they related to the Mahalanobis distance? Does it have something to do with changing the base in Linear Algebra etc.?  I have also read these former questions on the subject:       I have also read .  The answers are good and pictures nice, but still I don't really get it...I have an idea but it's still in the dark. Can someone give a "How would you explain it to your grandma"-explanation so that I could finally wrap this up and never again wonder what the heck is a Mahalanobis distance? :) Where does it come from, what, why?   UPDATE:   Here is something which helps understanding the Mahalanobis formula: Linux - Help, I'm running out of inodes! When you have a link from lets say twitter that is t.co/foo that links back to your website how does that effect SEO and how do the major search engines handle Shortened URLs? Where can I find sugar cane? I played several hours a started three different worlds in Minecraft, but I have never found any sugar canes. I read on Minecraft wiki to search near water but still no luck. Do you have more hints? Is it possible to re-create an environment that allow sugar canes to naturally grow? Variations in the pronunciation of "the" Although there are rather simple rules determining the pronunciation of "the", native speakers quite often deviate from these rules (including, e.g., TV shows). According to the Longman Pronunciation Dictionary,     The EFL learner is advised to use [ðə] before a consonant sound (the   boy, the house), [ði] before a vowel sound (the egg, the hour). Native   speakers, however, sometimes ignore this distribution, in particular   by using [ðə] before a vowel (which is in turn usually reinforced by a   preceding ʔ), or by using [ði:] in any   environment, though especially before a hesitation pause. Furthermore,   some speakers use stressed [ðə] as a strong form, rather than the   usual [ði:].   My question is: when native speakers use [ðə] instead of [ði] before a vowel sound, do they do it on purpose or accidentally? If it is on purpose, how do they (typically) decide which pronunciation to use? What is a valid reason to use [ðə] before a vowel sound? Is there a difference between DataTable.Clear and DataTable.Rows.Clear? Facebook must have changed something again because I cannot find out how to view the list of subscribers.  In Googling for this, I came upon this question:    However, it doesn't take me to my list os subscribers.  Where do I view this list now?  Please include a screenshot and highlight the link I need to click on.  This way, when Facebook changes their layout again, your screenshot will at least clue future inquirers in on this fact so they know they're not going crazy.  Edit  Here's what I see when I log into Facebook: Renaming files in lexicographical order with a numerical pattern that increases sequentially with fixed padding I have files such as  a bb ccc abc emrls   I would like to rename them so that, after sorting them (for example, lexicographically), each file gets the following name:  00001 00002 00003 etc   where the # of digits for the 0 padding is specified a priori, e.g. 6 in the case above (assuming that we know how many digits are needed).  Since the shell I am most comfortable with is zsh, I'm interested in solutions that benefit from features on zsh (maybe using zsh's zmv?). I would also be interested in solutions that are compatible with Bash. Prove Inverses not need be Unique if Associativity fails Let $M=\{x, y, z\}$ be a set and let $\circ$ be a binary operation on $M$ such that the identity element is $x$ and $y \circ y = x = y \circ z$. Prove that inverses need not be unique if associativity fails given the multiplication table below.  $x \circ x = x, x \circ y = y, x \circ z = z$  $y \circ x = y, y \circ y = x, y \circ z = x$  $z \circ x = z, z \circ y = x, z \circ z = x$ Why is $L^1(\mathbb{R}^n) \cap L^2(\mathbb{R}^n)$ dense in $ L^2(\mathbb{R}^n)$? Does anyone know why typedefs of class names don't work like class names for the friend declaration?  class A { public: };  class B : public A { public:    typedef A SUPERCLASS; };  typedef A X;  class C { public:    friend class A;             // OK    friend class X;             // fails    friend class B::SUPERCLASS; // fails }; GNU find and masking the {} for some shells - which? How to run a background task in a servlet based web application? List all files in all subfolders In windows, is there any way to get a list of all files in a folder, including all the files within all the subfolders? Occasionally I see an old Meta post that has no status tag (like ), but from the answers it looks like the question is resolved.  Example:  should be  since the answers say HTTP compression actually is enabled.  Is it worth flagging these questions, or is that a waste of time? Is just after your PhD a good time to switch your research area? I am finishing my PhD soon. The area in which I pursued my PhD is very challenging as I was only able to publish couple of papers even after spending many years. I want to switch into other research are due these reasons   to attract more students  to be comfortable to do research (along with teaching, I should be able to do research)   Even though I like the research I am doing right now, I seem to be isolated in my university. If ten students join my university for a PhD, hardly one student takes this area. My research area is not like machine learning or deep learning etc, so researchers of my domain are also not that much interested in my work.   The thing is I can work different research area but: Is this the right time? I am heading to a post-doc and learning a new area will probably take several months. Although my switch is not 180 degree, I am still worried. Why {are you / you are} making noise? What software to cite in a manuscript, and how? When writing a manuscript for a scientific article, I often wonder what software I should cite or acknowledge, and how.  The first problem is to make a choice which software to cite. On the one hand, there is no way to cite all software, as this would mean to cite my whole software stack (Linux, GNU tools, emacs, git, ...). On the other hand, not citing any software is not fair, either. Furthermore, some software explicitly asks to be cited, some software doesn't. Also, some software is really crucial to the results, some isn't. Another important aspect is that citing software is not only about giving credit to the authors of the software, but also to give other scientists hints on what software they might want to use. So, the choice which software to cite is a problem.  The second problem is how to cite the software. Some (scientific) software does provide a classical scientific article that can be cited. However, in this case, no URL to the software is given. Others do not have an associated article. How do I cite these? I have seen people that cite the manual of a software, others just give the URL. What is the way to go?  Another aspect is where to cite the software. Some software can be cited in the course of the articles text, but when it comes to more fundamental software, other places may be more appropriate.  Are there any good ideas out there on any of these aspects? A lot of textbooks and exam boards claim that light incident at exactly the critical angle is transmitted along the media boundary (i.e. at right-angles to the normal), but this seems to violate the principle of reversibility in classical physics.  How would a photon or ray travelling in the reverse direction "know" when to enter the higher refracting medium?  It can't know, so I conclude that such light is simply reflected?  Is this correct? How to delay or slowly loop commands? I found 11 questions like this on gamingSE already, but none of them have proper and up-to-date answers. So I'm creating this Q&amp;A:  How do you either activate a command x seconds/minutes/hours/… in the future or every x seconds/minutes/… in a loop?  Repeating command blocks and ticking functions execute 20 times per second, redstone is  in many situations and most of the extremely fancy solutions, like falling blocks in cobwebs, have broken over time or are needlessly complicated.