This question already has answers here:
multiplying all elements of a vector in R
(2 answers)
Closed 4 years ago.
How to use for loop to multiply every number in the given vector L = c(2,5,8,9,...n)?
Not quite sure how to multiply everything together..
L<-c(3,5,7,9)
for (n in L){
print(n)
}
Note that unlike some other languages, R makes a specific distinction between vectors and lists. Normally c(2, 5, 8, 9) as you've written produces a vector, which among other things, enables the use of prod:
L <- c(2, 5, 8, 9)
prod(L)
#> [1] 720
Created on 2018-09-21 by the reprex package (v0.2.0).
Related
This question already has answers here:
Sample from vector of varying length (including 1)
(4 answers)
Closed 3 years ago.
sample(x,n) The parameters are the vector, and how many times you wish to sample
sample(c(5,9),1) returns either 5 or 9
however,
sample(5,1) returns 1,2,3,4, or 5?
I've read the help section:
If x has length 1, is numeric (in the sense of is.numeric) and x >= 1,
sampling via sample takes place from 1:x. Note that this convenience
feature may lead to undesired behaviour when x is of varying length in
calls such as sample(x). See the examples.
But is there a way to make it not do this? Or do I just need to include an if statement to avoid this.
Or do I just need to include an if statement to avoid this.
Yeah, unfortunately. Something like this:
result = if(length(x) == 1) {x} else {sample(x, ...)}
Here's an alternative approach: you simply subset a random value from your vector like this -
set.seed(4)
x <- c(5,9)
x[sample(length(x), 1)]
[1] 9
x <- 5
x[sample(length(x), 1)]
[1] 5
This question already has answers here:
How to delete multiple values from a vector?
(9 answers)
Closed 5 years ago.
I have a vector called data which has approximately 35000 elements (numeric). And I have a numeric vector A. I want to remove every appearance of elements of A in the vector data. For example if A is the vector [1,2]. I want to remove all appearance of 1 and 2 in the vector data. How can I do that? Is there a built in function that does this? I couldn't think of a way. Doing it with a loop would take a long time I assume. Thanks!
There is this handy %in%-operator. Look it up, one of the best things I can think of in any programming language! You can use it to check all elements of one vector A versus all elements of another vector B and returns a logical vector that gives the positions of all elements in A that can be found in B. It is what you need! If you are new to R, it might seem a bit weird, but you will get very much used to it.
Ok, so how to use it? Lets say datvec is your numeric vector:
datvec = c(1, 4, 1, 7, 5, 2, 8, 2, 10, -1, 0, 2)
elements_2_remove = c(1, 2)
datvec %in% elements_2_remove
## [1] TRUE FALSE TRUE FALSE FALSE TRUE FALSE TRUE FALSE FALSE FALSE TRUE
So, you see a vector that gives you the positions of either 1 or 2 in datvec. So, you can use it to index what yuo want to retain (by negating it):
datvec = datvec[!(datvec %in% elements_2_remove)]
And you are done!
This question already has an answer here:
Why does the vector gets expanded in the loop
(1 answer)
Closed 6 years ago.
I am running into some behaviour with R that I find confusing. Does anyone have any insight into what is going on here?
Define two objects
i <- 5
nr <- 10
So i + 2 and nr + 1
> i+2
[1] 7
> nr+1
[1] 11
So to create a sequence from 7 to 11 I could do this:
7:11
But my question why does this not produce the same result?
i+2:nr+1
We already established above that it's input numbers are equivalent. Obviously I'm missing something here but I just don't know what it is.
You have just discovered the prime R gotcha, namely: 1:n-1 produces the sequence 0, 1, 2, ..., n-1.
To obtain what you desire, wrap the expressions in brackets:
1:(n-1)
or use
seq.int(1, n-1)
The reason for the issue is operator precedence - ?Syntax`
I'm new to R and I would be very grateful for an answer to my question:
I've got a vector: c(9, 11, 2, 6, 10) and the number 4 (or a vector c(4))
I want to generate a vector with the absolute difference between the first and the second one, which should look like this: c(5, 7, 2, 2, 6)
How do I do this? I can't get it to work with diff(), even after reading through the help (?diff()).
Any help is appreciated :)
x <- c(9, 11, 2, 6, 10)
abs(x - 4)
#[1] 5 7 2 2 6
abs finds the absolute value of a vector. '4' will be recycled when subtracted from x. If you have multiple values to be subtracted, they will also be recycled with a warning unless they are the same length as x.
You ran into problems with diff because it isn't designed for scalar subtraction (what you are attempting). It is better suited to finding the difference within a vector.
This question already has answers here:
Test if a vector contains a given element
(8 answers)
Closed 9 years ago.
Say I have a numerical vector in R. And I want to see if a particular integer is present in the vector or not. We can do that easily in python using 'in' command and an if statement may be.
Do we have something similar in R as well? So that I don't have to use a for loop to check if the integer I want is present in a vector? I tried the following, but it does not seem to work. 'normal' is a dataframe and the second column has integers.
if (12069692 in normal[,2]) {print("yes")}
Says,
Error: unexpected 'in' in "if (12069692 in"
In R, it's called %in%:
> 1 %in% c(1, 2, 3)
[1] TRUE
> 4 %in% c(1, 2, 3)
[1] FALSE
It is vectorized on the left-hand side, so you can check multiple values at once:
> c(1, 4, 2, 1) %in% c(1, 2, 3)
[1] TRUE FALSE TRUE TRUE
(hat tip #Spacedman)