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When data is "tidy," it is often organized into several tables. To combine the data for analysis, we need to "update" one table with values from another. For example, we might have sales data for performances, where attributes of the performer (their budget) and of the location ...

# example data a = data.table(id = c(1L, 1L, 2L, 3L, NA_integer_), x = 11:15) # id x # 1: 1 11 # 2: 1 12 # 3: 2 13 # 4: 3 14 # 5: NA 15 b = data.table(id = 1:2, y = -(1:2)) # id y # 1: 1 -1 # 2: 2 -2 Intuition Think of x[i] as selecting a subset of x for each row of i....

# example data DT = as.data.table(mtcars, keep.rownames = TRUE) To rearrange the order of columns, use setcolorder. For example, to reverse them setcolorder(DT, rev(names(DT))) This costs almost nothing in terms of performance, since it is just permuting the list of column pointers in the da...

# example data DT = as.data.table(mtcars, keep.rownames = TRUE) To rename a column (while keeping its data the same), there is no need to copy the data to a column with a new name and delete the old one. Instead, we can use setnames(DT, "mpg_sq", "mpq_squared") to modify ...

# example data DT = data.table(iris) To modify factor levels by reference, use setattr: setattr(DT$Species, "levels", c("set", "ver", "vir") # or DT[, setattr(Species, "levels", c("set", "ver", "vir"))] The sec...

# example data set.seed(1) n = 1e7 ng = 1e4 DT = data.table( g1 = sample(ng, n, replace=TRUE), g2 = sample(ng, n, replace=TRUE), v = rnorm(n) ) Matching on one column After the first run of a subsetting operation with == or %in%... system.time( DT[ g1 %in% 1:100] )...

Tuples support the following build-in functions Comparison If elements are of the same type, python performs the comparison and returns the result. If elements are different types, it checks whether they are numbers. If numbers, perform comparison. If either element is a number, then the other...

Introduction The PHPUnit Manual describes mocking as such: The practice of replacing an object with a test double that verifies expectations, for instance asserting that a method has been called, is referred to as mocking. So instead of stubbing out code, an observer is created that not onl...

// application/controllers/Company_controller.php <?php if(!defined('BASEPATH')) exit('No direct script access allowed'); class Company_controller extends CI_Controller { public function __construct() { parent::__construct(); $this->load->model('companies_mo...

To start GDB, in the terminal, gdb <executable name> For the above example with a program named main, the command becomes gdb main Setting Breakpoints You'll probably want you program to stop at some point so that you can review the condition of your program. The line at which you wan...

Batch file command line arguments are parameter values submitted when starting the batch. They should be enclosed in quotes if they contain spaces. In a running batch file, the arguments are used for various purposes, i.e. redirection to :labels, setting variables, or running commands. The argument...

Bottom sheets slide up from the bottom of the screen to reveal more content. They were added to the Android Support Library in v25.1.0 version and supports above all the versions. Make sure the following dependency is added to your app's build.gradle file under dependencies: compile 'com.android...

Assuming you have Eclipse IDE for Java Developers installed, start Eclipse, click "Help" -> "Install New Software..." Select "--All Available Sites--" at "Work with:", and navigate to "Eclipse Plugin Development Tools". Select "Eclipse Pl...

Automatic Linebreaks Table content is line wrapped automatically if it is too wide. In the following example, text is added to the second column, which causes oth the text itself and the column header of the first column to be wrapped. | this is a really wide column header | another header | | -...

io-streams is Stream-based library that focuses on the Stream abstraction but for IO. It exposes two types: InputStream: a read-only smart handle OutputStream: a write-only smart handle We can create a stream with makeInputStream :: IO (Maybe a) -> IO (InputStream a). Reading from ...

If an iteration method such as each is called without a block, an Enumerator should be returned. This can be done using the enum_for method: def each return enum_for :each unless block_given? yield :x yield :y yield :z end This enables the programmer to compose Enumerable operati...

Use rewind to restart the enumerator. ℕ = Enumerator.new do |yielder| x = 0 loop do yielder << x x += 1 end end ℕ.next # => 0 ℕ.next # => 1 ℕ.next # => 2 ℕ.rewind ℕ.next # => 0

There are two approaches for influencing when a memory cleanup is performed. They are influencing how often the automatic process is performed and the other is manually triggering a cleanup. The garbage collector can be manipulated by tuning the collection thresholds which affect the frequency at w...

Get the current date and time. public class Program { static void Main() { // create empty pipeline PowerShell ps = PowerShell.Create(); // add command ps.AddCommand("Get-Date"); // run command(s) Console.WriteLine(&quot...

HTML email is the use of a subset of HTML and CSS to format an email message like a web page using colors, graphics, table columns and links. When you send an email it’s important to send both plain text and HTML. You do this by sending your email as multi-part MIME. Most email service providers ha...