R语言中命名列表子列表值提取函数报错原因排查

Hey there! Let's break down exactly what's happening here:

The Core Issue: Literal vs. Variable Indexing #

When you changed tmp <- data[[i]] to tmp <- data[['i']], you made a critical shift in how R interprets the index:

• data[[i]] uses the value of the variable i (in your case, 8) to look up the element in the list. Depending on whether i is a number or string, this will either index by position or by the list's names.
• data[['i']] looks for an element with the literal string name "i" in your list. Your data object only has sublists named "4", "5", "6", "7", "8" — there's no sublist called "i"! So tmp ends up being NULL.

Why the Warning Happens #

When tmp is NULL, any operation that tries to access its elements (like lengths(tmp)) returns an empty vector. The min() function can't compute a minimum from an empty set of values, so it throws that warning: "min(lengths(tmp)): no non-missing arguments to min; returning Inf" and returns Inf. Since there's no valid data in tmp to sample from, your function ends up returning an empty list.

How to Fix It #

If you want to target the sublist corresponding to the value of i (e.g., 8 → the sublist named "8"), stick with the original syntax, or explicitly convert i to a character if you're passing a number:

# Option 1: Use the variable directly (works if i is a string, or if R can coerce it to match a name)
tmp <- data[[i]]

# Option 2: Explicitly convert numeric i to a character to match list names
tmp <- data[[as.character(i)]]

This will correctly grab the sublist you intended (the one named "8" when you call get_elements(data, 8)), and your sampling logic will work as expected.

内容的提问来源于stack exchange，提问作者user213544