How to create an empty R vector to add new items

Question

Hi, I want to use R in Python, as provided by the module Rpy2. I notice that R has very convenient [] operations by which you can extract the specific columns or lines, how could I achieve such a function by python scripts? My idea is to create a R vector and add those wanted elements into this vecotr so that the final vector is the same as that in R. As I am new to R, I create a seq(), but it seems that it has an initial digit 1, so the final result would always started with the digit 1, which is not what I want. So, is there a better way to do this? Thanks!

Answer 1

I pre-allocate a vector with

> (a <- rep(NA, 10))
 [1] NA NA NA NA NA NA NA NA NA NA

You can then use [] to insert values into it.

Answer 2

You can create an empty vector like so

vec <- numeric(0)

And then add elements using c()

vec <- c(vec, 1:5)

However as romunov says, it's much better to pre-allocate a vector and then populate it (as this avoids reallocating a new copy of your vector every time you add elements)

Answer 3

vec <- vector()

See also vector help

?vector

Answer 4

I've also seen

x <- {}

Now you can concatenate or bind a vector of any dimension to x

rbind(x, 1:10)
cbind(x, 1:10)
c(x, 10)

Answer 5

In rpy2, the way to get the very same operator as "[" with R is to use ".rx". See the documentation about extracting with rpy2

For creating vectors, if you know your way around with Python there should not be any issue. See the documentation about creating vectors