It looks like http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#526 addressed this problem (or something very similar to it) as a potential defect in the standard: 1) Parameters taken by const reference can be changed during execution of the function Examples: Given std::vector v: v.insert(v.begin(), v[2]); v[2] can be changed by moving elements of vector The proposed resolution was that this … Read more
One way is: for (vector<my_class>::reverse_iterator i = my_vector.rbegin(); i != my_vector.rend(); ++i ) { } rbegin()/rend() were especially designed for that purpose. (And yes, incrementing a reverse_interator moves it backward.) Now, in theory, your method (using begin()/end() & –i) would work, std::vector‘s iterator being bidirectional, but remember, end() isn’t the last element — it’s one … Read more
For space-optimization reasons, the C++ standard (as far back as C++98) explicitly calls out vector<bool> as a special standard container where each bool uses only one bit of space rather than one byte as a normal bool would (implementing a kind of “dynamic bitset”). In exchange for this optimization it doesn’t offer all the capabilities … Read more
Technically lists are vectors, although very few would use that term. “list” is one of several modes, with others being “logical”, “character”, “numeric”, “integer”. What you are calling vectors are “atomic vectors” in strict R parlance: aaa <- vector(“list”, 3) is.list(aaa) #TRUE is.vector(aaa) #TRUE Lists are a “recursive” type (of vector) whereas atomic vectors are … Read more
There have been many answers here and just about all of them will get the job done. However there is some misleading advice! Here are the options: vector<int> dataVec; int dataArray[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }; unsigned dataArraySize = sizeof(dataArray) / sizeof(int); // Method 1: Copy the … Read more
When you extract a single row from a data frame you get a one-row data frame. Convert it to a numeric vector: as.numeric(df[1,]) As @Roland suggests, unlist(df[1,]) will convert the one-row data frame to a numeric vector without dropping the names. Therefore unname(unlist(df[1,])) is another, slightly more explicit way to get to the same result. … Read more
a <- 1:120 b <- a[seq(1, length(a), 6)]
Once again, it seems I’ve answered my own question by getting impatient and asking it in #clojure on Freenode. Good thing answering your own questions is encouraged on Stackoverflow.com 😀 I had a quick discussion with Rich Hickey, and here is the gist of it. [12:21] <Raynes> Vectors aren’t seqs, right? [12:21] <rhickey> Raynes: no, … Read more
The structure std::vec::Vec has method append(): fn append(&mut self, other: &mut Vec<T>) Moves all the elements of other into Self, leaving other empty. From your example, the following code will concatenate two vectors by mutating a and b: fn main() { let mut a = vec![1, 2, 3]; let mut b = vec![4, 5, 6]; … Read more
Use the std::vector::vector(count, value) constructor that accepts an initial size and a default value: std::vector<std::vector<int> > fog( ROW_COUNT, std::vector<int>(COLUMN_COUNT)); // Defaults to zero initial value If a value other than zero, say 4 for example, was required to be the default then: std::vector<std::vector<int> > fog( ROW_COUNT, std::vector<int>(COLUMN_COUNT, 4)); I should also mention uniform initialization was … Read more