Creating simply correlated data in R

Although it might appear as a trivial task to a R user with 1 or 2 weeks of R experience, I thought that this might help to a total noob like me. It's fascinating how you can avoid using loops in R to get the jobs done in a few lines of code (or commands as one might argue...)

So you end up with a simple 2-D data set with some correlation, nothing fancy at all. Anyway, I needed this to play around with Principal Component Analysis (PCA), more on that later.

Rendering...

Comments

Detaching a process from terminal - exec(), system(), setsid() and nohup

Linux processes are created by fork() and exec(). The very first process of POSIX systems is init and subsequent processes are derived from the init as parent. These subsequent processes are child processes. During forking the parent process copies itself - with all I/O, address space, stack, everything. The only thing that is different is the process ID. The parent and child will have 2 different process IDs. The system() library function uses fork(2) to create a child process that executes the shell command specified in command using execl(3) as follows: execl("/bin/sh", "sh", "-c", command, (char *) 0); system() returns after the command has been completed. system() executes a command specified in command by calling /bin/sh -c command , and returns after the command has been completed. During execution of the command, SIGCHLD will be blocked, and SIGINT and SIGQUIT will be ignored. system() calls are often made within programs to execut...

sprintf, snprintf, strcpy, strncpy and sizeof operator

"C library functions such as strcpy (), strcat (), sprintf () and vsprintf () operate on null terminated strings and perform no bounds checking." "snprintf is safer than sprintf" What do these statements really mean? int sprintf ( char * str , const char * format , ... ) int snprintf ( char * s, size_t n, const char * format, ... ); char * strcpy ( char * destination, const char * source ); char * strncpy ( char * destination, const char * source, size_t num ); The usage is something like; char* msg1 = new char[10]; strcpy(msg1, "test"); // 1 char buffer[128]; sprintf(buffer, "%s", msg); //2 strcpy : Copies bytes until it finds a 0-byte in the source code. The string literal "test" has 4 characters and a terminating null character at end, therefore needs 5 characters at least on msg1. Is this dangerous? Yes, because if the source message is not null terminated it will read until a null character ...

Vaadin vs GWT

From Chapter 1 of book of Vaadin I quote the following. Vaadin Framework is a Java web application development framework that is designed to make creation and maintenance of high quality web-based user interfaces easy. Vaadin supports two different programming models: server-side and client-side . The server-driven programming model is the more powerful one . It lets you forget the web and program user interfaces much like you would program a desktop application with conventional Java toolkits such as AWT, Swing, or SWT. But easier. While traditional web programming is a fun way to spend your time learning new web technologies, you probably want to be productive and concentrate on the application logic. The server-side Vaadin framework takes care of managing the user interface in the browser and the AJAX communications between the browser and the server . With the Vaadin approach, you do not need to learn and deal directly with browser technologies, such as HTML or JavaScript. ...

Lost amongst the geeks

Search This Blog