Filtering a data frame on a vector
Filter data.frame rows by a logical condition
Cannot inherit from multiple classes defining __slots__? How to make a process invisible to other users? How could you launch a process and make it invisible to the top command? The process is started by a normal user (not root), and should not be visible to other normal users. How to kill a dragon in Skyrim? Anyone got any tips on how to beat down a Dragon solo? I've managed to get it down to 3/4 health, but keep running out of potions and getting owned.  I tend to whittle it down with bow from cover, then hit it with akimbo Lightning Strike which is awesome btw. Then poison and some sword.  I can't see a way to achieve this without having about 1000 points of stamina to run away from it when it does a swooping breath attack which seems to track you no matter what way you go.  Any advice please? This is for fighting them out in the open, "wild dragons" if you will. sample make file for creating more than one exe files with different directory Bash File Unable to locate package when new line is added When building a bash file to execute I keep getting an error after adding a new line. I have tried moving some lines around or removing some of the packages but it will results in the same error. In the file if I was to remove 3 and 4 it there will no longer be an error.   E: Unable to locate package &lt;package&gt;   The bash file looks like this   #!/usr/bin/env bash sudo apt update &amp;&amp; sudo apt install -y python3-pip build-essential python3-dev python3-setuptools gcc sshpass sudo apt-get install apt-transport-https lsb-release software-properties-common dirmngr sudo apt-get update   The output with the error  Hit:1 http://us.archive.ubuntu.com/ubuntu bionic InRelease Get:2 http://security.ubuntu.com/ubuntu bionic-security InRelease [88.7 kB]                                                   Hit:3 http://archive.ubuntu.com/ubuntu bionic InRelease                                             Get:4 http://us.archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB]         Get:5 http://us.archive.ubuntu.com/ubuntu bionic-backports InRelease [74.6 kB]                                       Fetched 252 kB in 1s (189 kB/s)     Reading package lists... Done Building dependency tree        Reading state information... Done All packages are up to date. Reading package lists... Done Building dependency tree        Reading state information... Done E: Unable to locate package sshpass Reading package lists... Done Building dependency tree        Reading state information... Done E: Unable to locate package dirmngr Hit:1 http://us.archive.ubuntu.com/ubuntu bionic InRelease Get:2 http://security.ubuntu.com/ubuntu bionic-security InRelease [88.7 kB]                                                   Hit:3 http://archive.ubuntu.com/ubuntu bionic InRelease                                             Get:4 http://us.archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB]         Get:5 http://us.archive.ubuntu.com/ubuntu bionic-backports InRelease [74.6 kB]                                       Fetched 252 kB in 1s (209 kB/s)     Reading package lists... Done Linux: clnt_create: RPC: Program not registered NFS mounts recently automatically got un-mounted. When I checked, the NFS service status it was shown to be running.  [root@hsluasrepo]# service nfs status rpc.svcgssd is stopped rpc.mountd (pid 4083) is running... nfsd (pid 4148 4147 4146 4145 4144 4143 4142 4141) is running... rpc.rquotad (pid 4079) is running...  [root@hsluasrepo]# service rpcbind status rpcbind (pid  4203) is running...  [root@hsluasrepo common]# rpcinfo -p 10.80.3.154    program vers proto   port  service     100000    4   tcp    111  portmapper     100000    3   tcp    111  portmapper     100000    2   tcp    111  portmapper     100000    4   udp    111  portmapper     100000    3   udp    111  portmapper     100000    2   udp    111  portmapper   But showmount output was showing an error.  [root@hsluasrepo ]# showmount -e 10.80.3.154 clnt_create: RPC: Program not registered   After restarting the NFS service, showmount output displayed the NFS server's export list.  Can anyone tell me the root cause of this issue and How to avoid this problem in future?  /var/log/messages:  Jul 7 03:22:01 hsluasrepo rsyslogd: [origin software="rsyslogd" swVersion="5.8.10" x-pid="1188" x-info="rsyslog.com"] rsyslogd was HUPed Jul 7 03:22:02 hsluasrepo rhsmd: In order for Subscription Manager to provide your system with updates, your system must be registered with RHN. Please enter your Red Hat login to ensure your system is up-to-date. Jul 8 03:22:01 hsluasrepo rhsmd: In order for Subscription Manager to provide your system with updates, your system must be registered with RHN. Please enter your Red Hat login to ensure your system is up-to-date. Jul 8 16:36:55 hsluasrepo kernel: nfsd: last server has exited, flushing export cache Jul 8 16:36:55 hsluasrepo rpc.mountd[4083]: Caught signal 15, un-registering and exiting. Jul 8 16:36:55 hsluasrepo rpc.mountd[24463]: Version 1.2.3 starting Jul 8 16:36:55 hsluasrepo kernel: NFSD: Using /var/lib/nfs/v4recovery as the NFSv4 state recovery directory Jul 8 16:36:55 hsluasrepo kernel: NFSD: starting 90-second grace period Jul 8 16:37:32 hsluasrepo rpc.mountd[24463]: authenticated mount request from 10.60.5.208:1004 for /common/PROD (/common/PROD) Jul 8 16:38:09 hsluasrepo rpc.mountd[24463]: authenticated mount request from 10.60.5.181:869 for /common/PROD (/common/PROD)  Jul 8 16:38:43 hsluasrepo rpc.mountd[24463]: authenticated mount request from 10.60.5.180:825 for /common/PROD (/common/PROD) Jul 8 16:39:12 hsluasrepo rpc.mountd[24463]: authenticated mount request from 10.60.5.176:688 for /common/PROD (/common/PROD) I'm writing code to do Xml serialization. With below function.  public static string SerializeToXml(object obj) {     XmlSerializer serializer = new XmlSerializer(obj.GetType());     using (StringWriter writer = new StringWriter())     {         serializer.Serialize(writer, obj);         return writer.ToString();     } }   If the argument is a instance of class without parameterless constructor, it will throw a exception.     Unhandled Exception:   System.InvalidOperationException:   CSharpConsole.Foo cannot be serialized   because it does not have a   parameterless constructor.    at   System.Xml.Serialization.TypeDesc.CheckSupported()   at   System.Xml.Serialization.TypeScope.GetTypeDesc(Type   type, MemberInfo sourc e, Boolean   directReference, Boolean throwOnError)   at   System.Xml.Serialization.ModelScope.GetTypeModel(Type   type, Boolean direct Reference)    at   System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(Type   type , XmlRootAttribute root, String   defaultNamespace)    at   System.Xml.Serialization.XmlSerializer..ctor(Type   type, String defaultName space)    at   System.Xml.Serialization.XmlSerializer..ctor(Type   type)   Why must there be a parameterless constructor in order to allow xml serialization to succeed?  EDIT: thanks for cfeduke's answer. The parameterless constructor can be private or internal. Motivating question:    I'm aware that one can construct a hierarchy of number systems via the Cayley–Dickson process:  $$\mathbb{R} \subset \mathbb{C} \subset \mathbb{H} \subset \mathbb{O} \subset \mathbb{S} \subset \ldots $$  "Reals" $\subset$ "Complex" $\subset$ "Quaternions" $\subset$ "Octonions" $\subset$ "Sedenions" $\subset$ $\ldots$  and that at each step you're given a multiplication table that tell how the elements interact. As you move up the ladder, certain "nice" properties are lost: ordering,  commutativity, associativity, multiplicative normedness, etc... Given the multiplication table, you can show that these properties don't hold.   Eric Naslund noted that "the first 4 are very special as they are the unique 4 normed division algebras over ℝ", no surprise then that these $2^n$-ions have found quite a bit of use. I'm interested in the sequence itself however, irrespective of how useful a $2^{256}$-ion might be (ducenti-quinquaginta-sex-ion?).   I feel like something deeper is going on here though that I don't understand. Why are these particular properties lost at each step? Is it possible to quantify the process such that, at the $2^n$-ion you can say something about the symmetry of the multiplication table*?  * I'm making an ansatz that there is a connection between the symmetry of the multiplication table and these "nice" properties. How to normalize data between -1 and 1? I have seen the min-max normalization formula but that normalizes values between 0 and 1. How would I normalize my data between -1 and 1? I have both negative and positive values in my data matrix. Possible Duplicate:          There are a lot of really screwed up configurations out there, because people didn't take a minute to sit down and think about something as simple as the name for their Active Directory forest. I'm asking this question to self-answer so that this knowledge can be more readily available. If you think you have a better answer, by all means add your input (but be prepared to defend it!)   So, what should I name my new Active Directory? Names of higher-order derivatives Specific derivatives have specific names. First order is often called tangency/velocity, second order is curvature/acceleration. I've also come across words like Jerk, Yank, Jounce, Jolt, Surge and Lurch for 3rd and 4th order derivatives. Is there a widely agreed list of names for these? How many orders have specific names?  In this case, I'm dealing with NURBs curves, so the "tangency" and "curvature" related words are to be preferred over "velocity" and "acceleration" words. How does Duff's device work? I've read the , and I don't get it. I am really interested, but I've read the explanation there a couple of times and I still don't get it how the Duff's device works.  What would a more detailed explanation be? JavaScript get clipboard data on paste event (Cross browser) What is the limit of $n \sin (2 \pi \cdot e \cdot n!)$ as $n$ goes to infinity? I tried and got this   $$e=\sum_{k=0}^\infty\frac{1}{k!}=\lim_{n\to\infty}\sum_{k=0}^n\frac{1}{k!}$$ $$n!\sum_{k=0}^n\frac{1}{k!}=\frac{n!}{0!}+\frac{n!}{1!}+\cdots+\frac{n!}{n!}=m$$ where $m$ is an integer. $$\lim_{n\to\infty}n\sin(2\pi en!)=\lim_{n\to\infty}n\sin\left(2\pi n!\sum_{k=0}^n\frac{1}{k!}\right)=\lim_{n\to\infty}n\sin(2\pi m)=\lim_{n\to\infty}n\cdot0=0$$  Is it correct? How do I generate random integers within a specific range in Java? How do I generate a random int value in a specific range? I have tried the following, but those do not work: Attempt 1: randomNum = minimum + (int)(Math.random() * maximum);  Bug: randomNum can be bigger than maximum. Attempt 2: Random rn = new Random(); int n = maximum - minimum + 1; int i = rn.nextInt() % n; randomNum =  minimum + i;  Bug: randomNum can be smaller than minimum. Solving $\textbf{r}''(t)=\frac{GM}{(r(t))^3}\textbf{r}(t)$ I have the following problem that I don't know how to solve:  Let $\textbf{r}(t)$ be a curve and let $r(t):= |\textbf{r}(t)|$. Let the curve $\textbf{r}(t)$ be defined by: $$\textbf{a}(t)=\frac{GM}{(r(t))^3}\textbf{r}(t)$$ Where $\textbf{a}(t) = \textbf{r}''(t)$ is the acceleration of the particle and $G,M \in \mathbb{R}$. Suppose that $\textbf{r}(t)$ and $\textbf{r}'(t)$ are not parallel. The objective is to determine the trajectory $\textbf{r}(t)$ in polar coordinates.  So basically we have the following equation: $$\textbf{r}''(t)=\frac{GM}{(r(t))^3}\textbf{r}(t)$$ The thing is that I don't know how I should proceed from now on. If we'd have just normal scalar function this would be a differential equation and I think I would be able to solve it, but like this I have no idea how to approach the problem. How can I solve this?  Edit: If $$\textbf{r}(t):=(x(t),y(t))$$ then the equation turns into the following system of equations: $$x''=\frac{GM}{(\sqrt{x^2 + y^2})^3}x$$ $$y''=\frac{GM}{(\sqrt{x^2 + y^2})^3}y$$ I don't know if this helps but I think that this turns thing easier perhaps. counting triangles in a graph or its complement Given a simple graph $G$ [no loops or parallel edges] on six vertices,  let $G^c$ denote its complement. It is known that either $G$ or $G^c$ must contain a triangle  $T$ in it. [An example of a Ramsey number I think.]   My question came up when I tried to find such a graph on six vertices  which had only one $T$ in it or its complement.  I believe if I did things right there are none of these. This I tried to check by drawing a copy of each graph $G$  on six vertices which has a $T$ in it,  and then looking at the complements to see if any had  no $T$'s in them. I found none.  One way to pose my question for a general number $n$ of vertices  is then as follows: Consider the set of all graphs $G$ on $n$ vertices,  and for each one construct $G^c.$  Count the number of $T$ in $G$ and add that to the number of $T$ in $G^c.$  Finally find the minimal such sum for the given $n$  and call that say $M(n).$ So my above six vertex conjecture  is that $M(6)=2.$   By considering a cycle graph on five vertices we find $M(5)=0.$   So going further one could ask if anything is known  about this minimum function $M(n)$ for larger $n$ [such as bounds, etc.] And does it have a name?  I would also like to see a simpler way to handle the six vertex case, one not involving drawing all the graphs. Why modules with no variables? My PC (Lenovo Ideapad z580) is overheating while running Ubuntu GNOME 16.04 LTS.  $ uname -a Linux Mahadev 4.4.0-72-generic #93-Ubuntu SMP Fri Mar 31 14:07:41 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux  $ lspci -nnk|grep -A2 VGA 00:02.0 VGA compatible controller [0300]: Intel Corporation 3rd Gen Core processor Graphics Controller [8086:0166] (rev 09)   Subsystem: Lenovo 3rd Gen Core processor Graphics Controller [17aa:3977]   Kernel driver in use: i915   $ sensors acpitz-virtual-0 Adapter: Virtual device temp1:        +52.0°C  (crit = +104.0°C)  coretemp-isa-0000 Adapter: ISA adapter Physical id 0:  +54.0°C  (high = +72.0°C, crit = +90.0°C) Core 0:         +54.0°C  (high = +72.0°C, crit = +90.0°C) Core 1:         +54.0°C  (high = +72.0°C, crit = +90.0°C)  update vivek@Mahadev:~$ stress -t 300 -c $(getconf _NPROCESSORS_ONLN) &amp;&amp;  sensors stress: info: [4408] dispatching hogs: 4 cpu, 0 io, 0 vm, 0 hdd stress: info: [4408] successful run completed in 300s acpitz-virtual-0 Adapter: Virtual device temp1:        +73.0°C  (crit = +104.0°C)  coretemp-isa-0000 Adapter: ISA adapter Physical id 0:  +72.0°C  (high = +72.0°C, crit = +90.0°C) Core 0:         +69.0°C  (high = +72.0°C, crit = +90.0°C) Core 1:         +72.0°C  (high = +72.0°C, crit = +90.0°C)  update     vivek@Mahadev:~$ sudo lshw -C cpu     [sudo] password for vivek:    *-cpu                             description: CPU         product: Intel(R) Core(TM) i3-3110M CPU @ 2.40GHz         vendor: Intel Corp.        physical id: 0        bus info: cpu@0        version: Intel(R) Core(TM) i3-3110M CPU @ 2.40GHz        serial: To Be Filled By O.E.M.        slot: CPU Socket - U3E1        size: 1302MHz        capacity: 2400MHz        width: 64 bits        clock: 100MHz        capabilities: x86-64 fpu fpu_exception wp vme de pse tsc msr  pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx  fxsr sse sse2 ss ht tm pbe syscall nx rdtscp constant_tsc arch_perfmon  pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni    pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm pcid    sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer xsave avx f16c lahf_lm    epb tpr_shadow vnmi flexpriority ept vpid fsgsbase smep erms xsaveopt     dtherm arat pln pts cpufreq           configuration: cores=2 enabledcores=2 threads=4  Update This time I edited the sensors , htop command result in image. It's getting overheated, my laptop is getting hang cause of overheating, please watch and reply. Thanks. Question  The test scores of three groups of people are saved as separate vectors in R.  set.seed(1) group1 &lt;- rnorm(100, mean = 75, sd = 10) group2 &lt;- rnorm(100, mean = 85, sd = 10) group3 &lt;- rnorm(100, mean = 95, sd = 10)   I want to know if there is a significant difference in the medians between these groups. I know that I could test group 1 versus group 2 using the Wilcoxon test, like so.  wilcox.test(group1, group2)   However, this compares only two groups at a time, and I would like to compare all three simultaneously. I would like a statistical test that yields a p value at the 0.05 significance level. Could someone please help?  Edit #1 - Mood's median test  Following user Hibernating's suggested answer, I tried Mood's median test.  median.test &lt;- function(x, y){     z &lt;- c(x, y)     g &lt;- rep(1:2, c(length(x), length(y)))     m &lt;- median(z)     fisher.test(z &lt; m, g)$p.value }  median.test(group1, group2)   However, this approach allows me to test for a significant difference between the medians of only two groups at a time. I am not sure of how to use it to compare the medians of all three simultaneously.  Edit #2 - Kruskal-Wallis test  User dmartin's suggested answer appears to be more or less what I need, and allows me to test all three groups simultaneously.  kruskal.test(list(group1, group2, group3))   Edit #3  User Greg Snow helpfully notes in his answer that the Kruskal-Wallis test is appropriate as long as it makes strict assumptions that make it also a test of means.