R <- Vector - Error in c(vector_item, v$Qty) : Object 'vector_item' not found

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A simple doubt,

How to have the (new) vector briefly to avoid: 

for(v in i$checkout) {
   c(vector, v$name) -> vector
   c(vector_item, v$qty) -> vector_item
}

Error in c(vector_item, v$Qty) : Object 'vector_item' not found

array r vector

  • vector_item already existed? Why do you only update like this in R if the object already exists... Try to create an empty vector or the size of v$qty before the for.

  • 1

    Can create vector_item <- NULL or vector_item <- c() before the cycle for.

1 answer

1


To solve the immediate problem, correct the error, as I say in the question comment can create the vector

vector_item <- NULL

or, alternatively,

vector_item <- c()

before the cycle for.

But it is very bad idea to extend the vectors within the cycles, it is very slow because it forces R to run the memory management routines as many times as the vector size changes.

It is much better to reserve memory before the cycle, creating a result vector of the appropriate length. See in this simple example the difference it makes. 

fun1 <- function(x){
  y <- NULL
  for(i in x){
    y <- c(y, 2*i)
  }
  y
}
fun2 <- function(x){
  y <- numeric(length(x))
  for(i in seq_along(x)){
    y[i] <- 2*x[i]
  }
  y
}

library(ggplot2)
library(microbenchmark)

n <- 1e3
x <- 1:n

mb <- microbenchmark(
  mem_extendida = fun1(x), 
  mem_reservada = fun2(x)
)

print(mb, order = 'median')
#Unit: microseconds
#          expr      min       lq      mean    median       uq      max neval cld
# mem_reservada  117.966  118.867  135.1909  137.0395  140.407  226.058   100  a 
# mem_extendida 2135.724 2187.807 2698.3200 2217.5420 2277.828 9311.886   100   b

autoplot(mb)

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  • worked, thank you very much

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