求助：开发R语言加密货币跨币种转换函数遇报错

Let's walk through the errors in your code and fix them step by step. I'll break down what's going wrong, explain the fixes, and give you a robust working version.

First, Let's Diagnose the Errors #

1. object 'x' not found / object 'z' not found #

This usually happens if you didn't pass arguments correctly when calling the function. For example:

• If you called convert(, 10, "Ethereum") (missing the first argument)
• Or mixed up the order of arguments, e.g., convert("Bitcoin", "Ethereum", 10) (you put the transfer amount last instead of second)
  Double-check that you're calling the function with the correct order: convert("转出货币名", 转出数量, "转入货币名")

2. attempt to select less than one element in get1index #

This error pops up when the currency name you passed doesn't exist in your mdata$id column. The which() function returns an empty vector when it can't find a match, and trying to grab [[1]] from an empty vector causes this crash. We need to add a check for this case.

3. Critical Logic Error in Conversion Calculation #

Your current calculation is doing this:

conversion <- currency_price[[index_z]] * amount
return(conversion / currency_price[[index_z]])

Which simplifies to just returning amount—that's why your function isn't actually converting anything! The correct formula for cross-currency conversion is:

转入数量 = (转出数量 × 转出货币单价) ÷ 转入货币单价

Fixed Function with Error Handling #

Here's the corrected version of your function, with safeguards and proper logic:

convert <- function(from_currency, amount, to_currency, data = mdata) {
  # Validate input amount is numeric
  if (!is.numeric(amount) || amount <= 0) {
    stop("Error: Amount must be a positive number!")
  }
  
  # Get price and ID columns from the dataset
  price_col <- data$current_price
  id_col <- data$id
  
  # Find indices for from and to currencies
  from_index <- which(id_col == from_currency)
  to_index <- which(id_col == to_currency)
  
  # Check if currencies exist in the dataset
  if (length(from_index) == 0) {
    stop(paste("Error: Currency", from_currency, "not found in the dataset!"))
  }
  if (length(to_index) == 0) {
    stop(paste("Error: Currency", to_currency, "not found in the dataset!"))
  }
  
  # Get the prices (take first match if there are duplicates)
  from_price <- price_col[[from_index[1]]]
  to_price <- price_col[[to_index[1]]]
  
  # Calculate conversion: total value in EUR / target currency price
  converted_amount <- (amount * from_price) / to_price
  
  return(converted_amount)
}

Key Improvements Explained #

• Descriptive Parameter Names: Changed x, z to from_currency, to_currency so the function is easier to read and use.
• Input Validation: Checks that amount is a positive number, and that both currencies exist in your dataset—this gives clear error messages instead of confusing crashes.
• Proper Conversion Logic: Implements the correct formula to calculate the amount of the target currency you'll get.
• Flexible Dataset Input: Added an optional data parameter so you can pass different datasets if needed (defaults to mdata for your use case).
• Handles Duplicates: If there are multiple entries with the same currency ID, it uses the first match (you can adjust this if needed for your dataset).

Example Usage #

If your mdata has "bitcoin" and "ethereum" in the id column, you can call the function like this:

convert(from_currency = "bitcoin", amount = 2, to_currency = "ethereum")

内容的提问来源于stack exchange，提问作者Giulia Montorsi