Rep() With Each Equals a Vector

rep() with each equals a vector

rep(1:5, vect1)

If you have questions about how to work functions in R, try

?function

where "function" is whatever function you want to know about. From ?rep you would have read:

'times' A integer vector giving the (non-negative) number of times to repeat
each element if of length length(x), or to repeat the whole vector if
of length 1. Negative or NA values are an error.

Recursively repeat vector elements N times each

rep(v, each=3)

or

rep(v, each=n)

where you have n defined

Create a repeating vector sequence using named vector of counts

rep( resp, times = counts)

Use the base function rep

Repeating elements in a vector with a for loop

Use the rep function, along with the possibility to use recycling logical indexing ...[c(TRUE, FALSE, TRUE, TRUE)]

rep(3:50, each = 2)[c(TRUE, FALSE, TRUE, TRUE)]

 ## [1]  3  4  4  5  6  6  7  8  8  9 10 10 11 12 12 13 14 14 15 16 16 17 18 18 19
## [26] 20 20 21 22 22 23 24 24 25 26 26 27 28 28 29 30 30 31 32 32 33 34 34 35 36
## [51] 36 37 38 38 39 40 40 41 42 42 43 44 44 45 46 46 47 48 48 49 50 50

If you use a logical vector (TRUE/FALSE) as index (inside [ ]), a TRUE leads to selection of the corresponding element and a FALSE leads to omission. If the logical index vector (c(TRUE, FALSE, TRUE, TRUE)) is shorter than the indexed vector (rep(3:50, each = 2) in your case), the index vector is recyled.

Also a side note: Whenever you use R code like

 x = c(x, something)

or

 x = rbind(x, something)

or similar, you are adopting a C-like programming style in R. This makes your code unnessecarily complex and might lead to low performance and out-of-memory issues if you work with large (say, 200MB+) data sets. R is designed to spare you those low-level tinkering with data structures.

Read for more information about the gluttons and their punishment in the R Inferno, Circle 2: Growing Objects.

Need help understandig the 'rep()' function

In R, rep is a function. It is designed to replicate its first argument a number of times equal to its second argument. Thus rep(2, 5) returns a vector of length 5 with each element as 2.

In R, functions are also objects, and when you input a function's name, R will return the something that tries to be useful by showing that the input is a function and providing the expected arguments. The .Primitive("rep") part tells you that rep is a primitive function, part of the base R code.

rep
function (x, ...)  .Primitive("rep")

In this case, rep requires at least one argument x, which the object to be replicated. The ... indicates that it can take a number of other optional arguments. To learn about them, you can access the help file for rep with ?rep.

You can call rep with more arguments, but the behavior might not be what you expect.

Create a vector by repeating values in a data frame

Adding comment as answer to help future users.

You can get this effect using rep like so:

x <- c(1,2,3)
y <- c(2,3,4)
vec <- rep(x, y)
vec
# [1] 1 1 2 2 2 3 3 3 3

How to know if a vector is composed by the same elements?

An option is diff.

diff(vec1)

If the elements are equal, their difference is zero.

all(diff(vec1) == 0)
#[1] TRUE

Or compare the vector to its first element.

all(vec1 == vec1[1])
#[1] TRUE

Edit.

Several ways of determining if all elements of a vector are equal were posted, see RHertel, Yuriy Saraykin, tmfmnk. Here are comparative tests.

library(microbenchmark)
library(ggplot2)

f <- function(n){
  x <- rep(10, n)
  mb <- microbenchmark(
    var = var(x) == 0,
    sd = sd(x) == 0,
    diff = all(diff(x) == 0),
    extract = all(x == x[1]),
    unique = length(unique(x)) == 1
  )
  mb
}

sizes <- c(10, 100, seq(1e3, 1e4, by = 1e3))
mb_list <- lapply(sizes, f)
names(mb_list) <- sizes

res <- lapply(seq_along(mb_list), function(i){
  agg <- aggregate(time ~ expr, mb_list[[i]], median)
  agg$size <- sizes[i]
  agg
})
res <- do.call(rbind, res)

ggplot(res, aes(size, time, colour = expr)) +
  geom_point() +
  geom_line()

Repeat down a column with an unequal number of values

How do I specific how many times a specific value repeats?

The times argument. From ?rep:

times
an integer-valued vector giving the (non-negative) number of times to repeat each element if of length length(x), or to repeat the whole vector if of length 1

> rep(c("Week 1", "Week 2", "Week 3"), times = c(10, 20, 30))
# repeats "Week 1" 10 times, "Week 2" 20 times, "Week 3" 30 times

Create vector with number of each type of item determined by another vector

We can use the rep function as well as seq.Date to do this:

Create Data

set.seed(123) 
kvec <- sample(0:10, 365, replace = T) #create the nonnegative integers
#create sequence of dates
date_vec <- seq.Date(from = as.Date('2015-01-01'), to = as.Date('2015-12-31'), by = 'day')

Use rep()

#let rep() do the work
k_date_vec <- rep(date_vec, times = kvec)

Result

head(kvec)
[1]  3  8  4  9 10  0
head(k_date_vec)
[1] "2015-01-01" "2015-01-01" "2015-01-01" "2015-01-02" "2015-01-02" "2015-01-02"

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