Add elements into a vector using loops and inputs

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I tried to write a simple command on R where the program asks 5 numbers for the user (input) and adds each one to a list. The problem is that the array is empty. I’ve tried lists too.

Follow the code below:

a <- c()

for(numero in 1:5){
  num <- as.numeric(readline(prompt = 'Numero: '))
  append(a,num)
}

print(a)
r

3 answers

4

vetor <- rep(NA, 5)

for (indice in seq_along(vetor)) {
  vetor[indice] <- as.numeric(readline(prompt = 'Numero: '))
}

print(vetor)

It is good practice in R not to create objects that expand in size; it is better to create the object already with the final size and use indexing to fill it.

  • And if I do not know a priori how much data I will store in the vector? For example, let’s assume that I will filter all averages with size may 15 of a given vector but I don’t know how many are a priori? In this case, the only way I see to store these values greater than 15 is to add them to an array. I don’t know if it’s because I’m more used to Python where it’s common to add elements in lists, but my reasoning is this.

  • 1

    This is a very long topic to answer here. If you read English, see chapter 2 of The R Inferno. Take advantage and read chapter 3, because it is also good to avoid loops in R. Well, read the whole book, which is excellent.

3

a <- c()

for(numero in 1:5){
  a <- append(a,numero)
}

print(a)

-You have to store the vector inside somewhere when you are running the "append". The function gives a return, this return needs to be stored somewhere.

  • In this case what I would like to do is different. I would like to add 5 numbers typed by the user in the list, and not simply number 1 to 5

  • I just managed to input and add elements to the array, disregard the previous question, thank you.

2

A way without cycles for is to read from stdin() with the function scan. Just pass the total numbers read in the argument n.

a <- scan(stdin(), what = character(), n = 5, quiet = TRUE)
a <- as.numeric(a)
print(a)

Note that scan reads numbers if the argument what does not change this. The problem is that if the user deceives and type something non-numerical the scan ends with error. If characters are read and then transformed into numbers this error no longer occurs.

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