I got this residuals vs fitted values plot.    As you can see there are some clear patterns of linearity. My guess is that the response depend on another variable that acts as a parameter to obtain theses lines, ie: the response should be better described as something of the form:  $$ Y = \alpha Z \cdot g(X) + e $$  for a $Z$ fixed one would obtain one of the lines we see in the plot.  What would you think ?  Edit: Sample of the dataset.  &gt;Boston[1:25,]       crim   zn indus chas   nox    rm   age    dis rad tax ptratio  black 1  0.00632 18.0  2.31    0 0.538 6.575  65.2 4.0900   1 296    15.3 396.90 2  0.02731  0.0  7.07    0 0.469 6.421  78.9 4.9671   2 242    17.8 396.90 3  0.02729  0.0  7.07    0 0.469 7.185  61.1 4.9671   2 242    17.8 392.83 4  0.03237  0.0  2.18    0 0.458 6.998  45.8 6.0622   3 222    18.7 394.63 5  0.06905  0.0  2.18    0 0.458 7.147  54.2 6.0622   3 222    18.7 396.90 6  0.02985  0.0  2.18    0 0.458 6.430  58.7 6.0622   3 222    18.7 394.12 7  0.08829 12.5  7.87    0 0.524 6.012  66.6 5.5605   5 311    15.2 395.60 8  0.14455 12.5  7.87    0 0.524 6.172  96.1 5.9505   5 311    15.2 396.90 9  0.21124 12.5  7.87    0 0.524 5.631 100.0 6.0821   5 311    15.2 386.63 10 0.17004 12.5  7.87    0 0.524 6.004  85.9 6.5921   5 311    15.2 386.71 11 0.22489 12.5  7.87    0 0.524 6.377  94.3 6.3467   5 311    15.2 392.52 12 0.11747 12.5  7.87    0 0.524 6.009  82.9 6.2267   5 311    15.2 396.90 13 0.09378 12.5  7.87    0 0.524 5.889  39.0 5.4509   5 311    15.2 390.50 14 0.62976  0.0  8.14    0 0.538 5.949  61.8 4.7075   4 307    21.0 396.90 15 0.63796  0.0  8.14    0 0.538 6.096  84.5 4.4619   4 307    21.0 380.02 16 0.62739  0.0  8.14    0 0.538 5.834  56.5 4.4986   4 307    21.0 395.62 17 1.05393  0.0  8.14    0 0.538 5.935  29.3 4.4986   4 307    21.0 386.85 18 0.78420  0.0  8.14    0 0.538 5.990  81.7 4.2579   4 307    21.0 386.75 19 0.80271  0.0  8.14    0 0.538 5.456  36.6 3.7965   4 307    21.0 288.99 20 0.72580  0.0  8.14    0 0.538 5.727  69.5 3.7965   4 307    21.0 390.95 21 1.25179  0.0  8.14    0 0.538 5.570  98.1 3.7979   4 307    21.0 376.57 22 0.85204  0.0  8.14    0 0.538 5.965  89.2 4.0123   4 307    21.0 392.53 23 1.23247  0.0  8.14    0 0.538 6.142  91.7 3.9769   4 307    21.0 396.90 24 0.98843  0.0  8.14    0 0.538 5.813 100.0 4.0952   4 307    21.0 394.54 25 0.75026  0.0  8.14    0 0.538 5.924  94.1 4.3996   4 307    21.0 394.33
The following is the residuals vs predicted scatter plot for a regression model with two IVs.   Initially, I thought it was evidence of heteroskedasticity. But, I reasoned that although there is a visible pattern in the plot, the variance across different levels of predicted values is same.  To clear my doubts, I saved the standardized residual and predicted values and ran a bi-variate correlation test. The correlation is zero, as expected. I am, nevertheless, intrigued by this observation. Any idea why I might have obtained this pattern?  PS:- My dependent variable is a sum of two likert-type items (Response scale: 1-5). So, it's theoretical range is 2-10 and it has no absolute zero value.
What is the new turbo boost in the MacBook line? The new MacBook line has a new turbo boost added to the processor:     2.3GHz Quad-core Intel Core i7, Turbo Boost up to 3.3GHz   What exactly does this mean? From what I've heard, the processor can runs above the clocked speed for a short period of time.  How does it work? I'm having trouble writing a regular expression that matches valid IPv6 addresses, including those in their compressed form (with :: or leading zeros omitted from each byte pair).    Can someone suggest a regular expression that would fulfill the requirement?  I'm considering expanding each byte pair and matching the result with a simpler regex. I am using Google Chrome 48.0 32-bit. Today when I launched Google Chrome, I got this message:    This computer will soon stop receiving Google Chrome updates because this Linux system will no longer be supported   I thought Ubuntu 14.04 is supported for five years, what's exactly happening here?  And on 64-bit Ubuntu, I get an error from Update Manager and apt-get update:  Failed to fetch http://dl.google.com/linux/chrome/deb/dists/stable/Release  Unable to find expected entry 'main/binary-i386/Packages' in Release file (Wrong sources.list entry or malformed file)   Some index files failed to download.   They have been ignored, or old ones used instead. If low-cost index funds are considered the best investment, why are there so many high-cost, managed funds? The general consensus is that the single best indicator of a fund's future performance is the its expense ratio . If you look for more than 5 minutes online you discover the  approach to investing; the , etc. It looks like the less you pay for a fund (and therefore the less it's managed), the better it does in the long run.  So why is it that in peoples' 401(k)s there are so many high-cost actively managed funds? Furthermore, why are there so many high-cost actively managed funds in the first place? Shouldn't the market reflect the fact that actively-managed funds typically don't beat the index they benchmark to and and react by purging itself of these crappy funds? Removing elements with Array.map in JavaScript I would like to filter an array of items by using the map() function. Here is a code snippet:  var filteredItems = items.map(function(item) {     if( ...some condition... )     {         return item;     } });   The problem is that filtered out items still uses space in the array and I would like to completely wipe them out.  Any idea?  EDIT: Thanks, I forgot about filter(), what I wanted is actually a filter() then a map().  EDIT2: Thanks for pointing that map() and filter() are not implemented in all browsers, although my specific code was not intended to run in a browser. text processing rows to columns for a block how to make a full backup of ubuntu server for another computer? I have a Ubuntu 15.10 server, which currently has a bunch of software installed on. Now, I want to make a full backup of everything there (including profiles, configs, etc...) on this computer (virtually on Parallels Desktop) for another physical computer which I've recently installed Ubuntu 15.10 server on it.  So how can I transfer this system completely into that computer? I tried PinguyBuilder and Systemback, but they were not what I wanted.  Considering that if there is a way, which would need not or at least a Internet connection (specially on physical computer) would be awesome.  Any help?  P.S: I know there are many topics for backup things, but they are not exactly for a non-gui server, or maybe I couldn't find what is suitable for me. How to use "grep" command to find text including subdirectories I want to find all files which contain a specific string of text. The grep command works, but I don't know how to use it for every directory (I can only do it for my current directory). I tried reading man grep, but it didn't yield any help. How is MSE divided by $\sigma^2$ always a chi-square distribution? Intuitive analysis of gradient, divergence, curl the output when I start firefox from Terminal I know SO's policy is &quot;you don't have to register to ask questions,&quot; but there are so many new members and so many hit-and-runs... The majority of the questions I see now are coming from new users (i.e., it's their first question). Although unregistered users should still be able to ask questions, I think we should encourage users to create an account. Here is a couple of ways we could do that:  Explicitly encourage people to get an account: there's currently nothing telling people to do that. Maybe tell people something like &quot;Get an account, it's easy!&quot; and maybe show some of the perks of having an account (and having rep).  Maybe give a few bonus points for registering; and have that enable a basic privilege. It could be taken from one of the , for example.   Of course getting people to register is just half of the battle. I don't know what the stats are on this, but I think there's a number of users who create multiple accounts anyways. We could curb that by:  Having smart(er)? duplicate account detection systems, alerting someone who is about to create a new account and possibly has an account already. Give them a message like &quot;Hey, it looks like you already have  account, are you sure you want to create a new one?&quot;  Create a new privilege (10k? 20k?) that gives users tools to detect possible duplicate accounts, eg: &quot;List users with the same e-mail,&quot; &quot;List users with the same IP addresses,&quot;  etc. (without revealing said emails and IPs). Then the 10k/20k can look at other stuff (e.g.: posts) and refer the new user to a moderator for a possible merge. What is the subject of this sentence I've seen this sentence in someone's facebook status but it sounds unnatural to me.     I'm the Rumplestiltskin who spins straw into gold   I thought it should be spin because the subject is I, but I'm not sure. Which one is the subject in this sentence, I or Rumplestiltskin and why? Why is the installer not showing any partitions? I'm having a problem installing Ubuntu, and Kali as well. I downloaded the iso from the official site &amp; tried installing using USB. I also tried desktop installation, but the problem is same.  It shows a single drive i.e. my total Hard Disk and if I select it, it asks me to create a new partition &amp; shows total space as FREE.  It's with all Ubuntu I downloaded, 11.10 Server, 12.10 and 13.04. I also tried to install BackTrack's new version Kali Linux but again I got the same problem.  I hope I meet thier system requirements. Here's my system details for your ease:   OS: Windows 7 Ultimate Processor: Intel P4 2.80 GHz RAM: 3GB Hard Disk: 320GB No of Local Drives: 4 (1 Primary, 3 Logical) Free Space: 195GB (about) Motherboard: G31 Cache: 1MB Help me, please. How to convert a 3 column csv file into a table (or matrix) I have an CSV input file format like this, with a nucleotide sequence in field 1, text in field 2, and an integer in field 4:  ATGC,CD3,56 ATGC,CD4,67 ATGC,IgD,126 ATGC,IgM,127 AGTC,CD3,67 AGTC,CD4,78 AGTC,IgD,102 AGTC,IgM,89 TCGA,CD3,334 TCGA,CD4,123 TCGA,IgD,456 TCGA,IgM,80 CGTA,CD3,54 CGTA,CD4,32 CGTA,IgD,82 CGTA,IgM,117   I opened this CSV file using Numbers in Mac it's display as 3 columns format, however, I want to convert it to the table(or Matrix) format (also a CSV file), making the first column, the nucleotide sequences, into a header, and want the result to also look like a table (or Matrix):       ATGC  AGTC  TCGA  CGTA CD3  56    67    334   54 CD4  67    78    123   32 IgD  126   102   456   82 IgM  127   89    80    117   Below is a section from my real input CSV file (sample input.txt):  AGAATAGTCTGATTCT,-,,38 AGAATAGTCTGATTCT,AnnexinV,,51 AGAATAGTCTGATTCT,CD127,,39 AGAATAGTCTGATTCT,CD138,,3 AGAATAGTCTGATTCT,CD14,,2 AGAATAGTCTGATTCT,CD16,,4 AGAATAGTCTGATTCT,CD19,,10 AGAATAGTCTGATTCT,CD20,,6 AGAATAGTCTGATTCT,CD24,,21 AGAATAGTCTGATTCT,CD25,,4 AGAATAGTCTGATTCT,CD27,,87 AGAATAGTCTGATTCT,CD3,,235 AGAATAGTCTGATTCT,CD34,,5 AGAATAGTCTGATTCT,CD38,,18 AGAATAGTCTGATTCT,CD4,,412 AGAATAGTCTGATTCT,CD43,,99 AGAATAGTCTGATTCT,CD5,,430 AGAATAGTCTGATTCT,CD56,,3 AGAATAGTCTGATTCT,CD8,,7 AGAATAGTCTGATTCT,IgD,,4 AGAATAGTCTGATTCT,IgM,,2 TGTGGTAGTTCGTCTC,-,,9 TGTGGTAGTTCGTCTC,AnnexinV,,42 TGTGGTAGTTCGTCTC,CD127,,6 TGTGGTAGTTCGTCTC,CD138,,4 TGTGGTAGTTCGTCTC,CD16,,40 TGTGGTAGTTCGTCTC,CD19,,7 TGTGGTAGTTCGTCTC,CD20,,2 TGTGGTAGTTCGTCTC,CD24,,24 TGTGGTAGTTCGTCTC,CD25,,2   How can I do this using Linux text formatting commands? I know that contents of double quotes are expanded, whereas the contents of single quotes are not, such that  echo '$1'   gives  $1   where as   echo "$1"   gives  &lt;the argument - blank in this particular example&gt;   the same as   echo $1   However, the question  led me to wonder why double quotes and not single quotes were used when declaring the alias, thus:  alias cutf="_cutf"   instead of   alias cutf='_cutf'   I would have employed single quotes as in the latter example. Most examples on the web use single too, unless there is some expansion required. However, in this case, no expansion, to my eyes, is apparent. Is it that, in this case, they are interchangeable, or are the double quotes necessary because a function definition is employed? How do you reverse a string in place in C or C++? How do you reverse a string in C or C++ without requiring a separate buffer to hold the reversed string? Bibliography with BibLaTeX: Do not abbreviate first given (first) name and abbreviate all further given names The first given name of an author or editor in my bibliography should be written out, but all further first names should be abbreviated (initials with a period -- and space if there are multiple first names/initials, see below). I am using style=authoryear with BibLaTeX (v. 2.7) and Biber (v. 1.7).  My bibliography looks like this:     Doe, John Arthur Kyle (2013). The secret life of John Doe.   It should look like this:     Doe, John A. K. (2013). The secret life of John Doe.   Minimal example:  example.tex  \documentclass{scrartcl}  \usepackage[ngerman]{babel} \usepackage[babel,german=quotes]{csquotes} \usepackage[backend=biber,style=authoryear]{biblatex} \bibliography{bibliography}  \begin{document}  \cite[123]{Doe} \printbibliography  \end{document}   bibliography.bib  @book{Doe,     title = {The secret life of John Doe},     author = {Doe, John Arthur Kyle},     year = {2013} }   (Worked with said versions of BibLaTeX and Biber, Texmaker (v. 4.0.3) and MiKTeX (v. 2.9.4813).)  I could not find a solution in biblatex.def and firstinits=true abbreviates all first names, including the first one. I understand that the expressions on both sides of an equal sign are the same entity, and I know that when you modify one side, the other must be changed because it is referring to the same thing. What I do not understand is why making a new equation (adding or taking away from an expression) allows one to know what an unknown represents. What about equations lets us do this? I've somehow lost my id_rsa.pub file. I still have my id_rsa file. How do I recover the public key from the private key?  (This question came up after ssh-copy-id was reporting "ERROR: No identities found" while ssh-keygen reported "/root/.ssh/id_rsa already exists". ls ~/.ssh pointed out the problem was having id_rsa but not id_rsa.pub. I found the solution, but it was buried at the bottom of a long post on an Ubuntu support forum.)