如何在R语言循环中使用get函数为向量追加新值？

Great question! The assign() function does have that annoying quirk where it overwrites existing objects instead of appending to them. Luckily, pairing it with get() lets you safely update vectors by first grabbing their current state, adding your new values, then saving the updated version back.

Step-by-Step Example #

First, let's set up our initial setup (with a fix to avoid overwriting right away):

set.seed(11)
my_future_vectors <- c("vec1", "vec2", "vec3")

# Initialize empty vectors if they don't exist yet
for (vec_name in my_future_vectors) {
  if (!exists(vec_name)) {
    assign(vec_name, numeric(0)) # Start with an empty numeric vector
  }
}

# Now append values to each vector in a loop
for (vec_name in my_future_vectors) {
  # Grab the current state of the vector
  current_values <- get(vec_name)
  # Add new values (here we're adding 3 random numbers between 0 and 1)
  updated_values <- c(current_values, runif(3, 0, 1))
  # Save the updated vector back to its original name
  assign(vec_name, updated_values)
}

Testing the Append Functionality #

If you want to manually append a specific value (like 1 to vec1), you can do this without overwriting:

# Append 1 to vec1
assign("vec1", c(get("vec1"), 1))

# Check the result - vec1 will have its original 3 random numbers plus 1
vec1

Key Notes #

• Initialize first: Starting with empty vectors ensures you don't get an error when trying to get() a vector that hasn't been created yet.
• Use c() or append(): Both work for combining existing and new values. append() is sometimes more readable if you want to specify where to add the new values (e.g., append(current_values, new_values, after = length(current_values))).
• Environment awareness: If you're working inside a function, make sure you specify the environment in get() and assign() (using the envir argument) to avoid accidentally modifying the global environment.

内容的提问来源于stack exchange，提问作者Alexandros