concatenation

I want to concatenate in the middle of an echo to write an if statement, is this possible? Here is what I have. echo "<li class='".if ($_GET["p"] == "home") { echo "active"; }."'><a href='#'>Home</a> </li>"; Like this, using the ternary operator : echo "<li class='". (($_GET["p"] == "home") ? "active" : "") . "'><a href='#'>Home</a> </li>"; Do like this: echo "<li class='".($_GET["p"] == "home" ? 'active' : '') ."'><a href='#'>Home</a> </li>"; echo "<li class='".(($_GET["p"] == "home") ? "active" : "")."'><a href='#'>Home</a> </li>"; Instead of messy inline concatenations, might I suggest

I have a data.frame from this code: my_df = data.frame("read_time" = c("2010-02-15", "2010-02-15", "2010-02-16", "2010-02-16", "2010-02-16", "2010-02-17"), "OD" = c(0.1, 0.2, 0.1, 0.2, 0.4, 0.5) ) which produces this: > my_df read_time OD 1 2010-02-15 0.1 2 2010-02-15 0.2 3 2010-02-16 0.1 4 2010-02-16 0.2 5 2010-02-16 0.4 6 2010-02-17 0.5 I want to average the OD column over each distinct read_time (notice some are replicated others are not) and I also would like to calculate the standard deviation, producing a table like this: > my_df read_time OD stdev 1 2010-02-15 0.15 0.05 5 2010-02-16 0.3

I have three matrices, each of size 4x1 . I want to copy all of these matrices to another matrix of size 4x3 and call it R . Is there a smart way to do it? You can just use hconcat for horizontal concatenation. You can use it per matrix, e.g. hconcat( mat1, mat2, R ), or apply it directly on a vector or array of matrices. Here's a sample code: vector<Mat> matrices = { Mat(4, 1, CV_8UC1, Scalar(1)), Mat(4, 1, CV_8UC1, Scalar(2)), Mat(4, 1, CV_8UC1, Scalar(3)), }; Mat R; hconcat( matrices, R ); cout << R << endl; Here's the result: [1, 2, 3; 1, 2, 3; 1, 2, 3; 1, 2, 3] Program ended with exit

This question already has an answer here: How to concatenate factors, without them being converted to integer level? 8 answers I want to concatenate two vectors one after the other in R. I have written the following code to do it: > a = head(tracks_listened_train) > b = head(tracks_listened_test) > a [1] cc1a46ee0446538ecf6b65db01c30cd8 19acf9a5cbed34743ce0ee42ef3cae3e [3] 9e7fdbf2045c9f814f6c0bed5da9bed7 3441b1031267fbb6009221bf47f9c5e8 [5] 206c8b79bd02beeea200879afc414879 1a7a95e3845a6815060628e847d14362 18585 Levels: 0001a423baf29add84af6ec58aeb5b90 ... > b [1]

Please correct me if i'm wrong. In Java 8, for performance reasons, when concatenating several strings by the "+" operator StringBuffer was invoked. And the problem of creating a bunch of intermediate string objects and polluting the string pool was "resolved". What about Java 9? There'a new feature added as Invokedynamic. And a new class that resolves the problem even better, StringConcatFactory. String result = ""; List<String> list = Arrays.asList("a", "b", "c"); for (String n : list) { result+=n; } My question are: How many objects are created in this loop? Are there any intermedier

I'm trying to implement a method to concatenate multiple List s e.g. List<string> l1 = new List<string> { "1", "2" }; List<string> l2 = new List<string> { "1", "2" }; List<string> l3 = new List<string> { "1", "2" }; var result = Concatenate(l1, l2, l3); but my method doesn't work: public static IEnumerable<T> Concatenate<T>(params IEnumerable<T> List) { var temp = List.First(); for (int i = 1; i < List.Count(); i++) { temp = Enumerable.Concat(temp, List.ElementAt(i)); } return temp; } Use SelectMany : public static IEnumerable<T> Concatenate<T>(params IEnumerable<T>[] lists) { return lists