R语言quantmod绘制股票折线图时图例无法显示的求助

问题描述 #

尝试为AAPL股价走势图添加图例框，标注各颜色线条对应的股价类型（开盘价、收盘价等），但多次尝试后图例始终无法显示。

已尝试的解决方法：

• 修改legend()函数的x、y参数值
• 将图表导出为PDF或JPG格式
• 执行dev.off()重启图形驱动并更新相关库
• 刷新图表预览

期望效果：显示图例框，明确标注蓝色、红色、绿色、橙色、紫色线条分别代表开盘价、收盘价、调整后价格、最高价、最低价。

原代码 #

#install.packages("quantmod")
library(quantmod)

symbol <- "AAPL"
start_date <- as.Date("2023-04-11")
end_date <- as.Date("2023-05-11")


getSymbols(Symbols = symbol, src = "yahoo", from = start_date, to = end_date)
opening_prices <- stock_data[, paste(symbol, "Open", sep = ".")]
closing_prices <- stock_data[, paste(symbol, "Close", sep = ".")]
adjusted_prices <- stock_data[, paste(symbol, "Adjusted", sep = ".")]
high_prices <- stock_data[, paste(symbol, "High", sep = ".")]
low_prices <- stock_data[, paste(symbol, "Low", sep = ".")]
volume <- stock_data[, paste(symbol, "Volume", sep = ".")]

#this would print default table of stock data
#print(stock_data)

stock_data_df <- data.frame(
  opening_prices, 
  closing_prices, 
  adjusted_prices, 
  high_prices, 
  low_prices, 
  volume
)

print(stock_data_df)

# Create a new plot with the opening prices
plot(opening_prices, type = "l", col = "blue", main = paste("Stock Prices for", symbol))

# Add lines for closing, adjusted, high, and low prices
lines(closing_prices, type = "l", col = "red")
lines(adjusted_prices, type = "l", col = "green")
lines(high_prices, type = "l", col = "orange")
lines(low_prices, type = "l", col = "purple")

legend(x = "topright",
       legend = c("Opening Prices", "Closing Prices", "Adjusted Prices", "High Prices", "Low Prices"), 
       lty = c(1, 1, 1, 1, 1),
       col = c("blue", "red", "green", "orange", "purple"))

当前输出情况 #

• R Studio图表输出：仅显示AAPL股价走势的多条彩色线条，右上角无预期的图例框
• dput(opening_prices)输出：返回xts格式的时间序列数据，包含日期与对应开盘价数值

问题原因及解决方法 #

核心原因 #

quantmod包返回的是xts时间序列对象，其自带的plot.xts()函数会创建特殊的绘图区域，基础绘图系统的legend()无法正确识别该区域，导致图例不显示。此外原代码中stock_data变量未定义（getSymbols默认将数据存入以symbol命名的变量AAPL），也会引发报错。

方法1：使用quantmod自带的图例绑定方式 #

通过addTA()添加线条，并在legend()中指定on=1绑定到主绘图区域：

#install.packages("quantmod")
library(quantmod)

symbol <- "AAPL"
start_date <- as.Date("2023-04-11")
end_date <- as.Date("2023-05-11")

# getSymbols默认将数据存入变量AAPL
getSymbols(Symbols = symbol, src = "yahoo", from = start_date, to = end_date)
opening_prices <- AAPL[, paste(symbol, "Open", sep = ".")]
closing_prices <- AAPL[, paste(symbol, "Close", sep = ".")]
adjusted_prices <- AAPL[, paste(symbol, "Adjusted", sep = ".")]
high_prices <- AAPL[, paste(symbol, "High", sep = ".")]
low_prices <- AAPL[, paste(symbol, "Low", sep = ".")]

# 用quantmod绘图系统创建主图
plot(opening_prices, type = "l", col = "blue", main = paste("Stock Prices for", symbol))
# 添加其他线条到主图区域
addTA(closing_prices, type = "l", col = "red", on=1)
addTA(adjusted_prices, type = "l", col = "green", on=1)
addTA(high_prices, type = "l", col = "orange", on=1)
addTA(low_prices, type = "l", col = "purple", on=1)

# 绑定主图区域添加图例
legend("topright",
       legend = c("Opening Prices", "Closing Prices", "Adjusted Prices", "High Prices", "Low Prices"),
       lty = 1,
       col = c("blue", "red", "green", "orange", "purple"),
       on=1)

方法2：转换为数据框使用基础绘图系统 #

将xts对象转为普通数据框，手动处理x轴，让基础绘图系统的legend()正常工作：

#install.packages("quantmod")
library(quantmod)

symbol <- "AAPL"
start_date <- as.Date("2023-04-11")
end_date <- as.Date("2023-05-11")

getSymbols(Symbols = symbol, src = "yahoo", from = start_date, to = end_date)
# 转换为带日期列的数据框
stock_data_df <- data.frame(
  Date = index(AAPL),
  Open = AAPL$AAPL.Open,
  Close = AAPL$AAPL.Close,
  Adjusted = AAPL$AAPL.Adjusted,
  High = AAPL$AAPL.High,
  Low = AAPL$AAPL.Low
)

# 基础绘图系统绘制
plot(stock_data_df$Open ~ stock_data_df$Date, type = "l", col = "blue",
     main = paste("Stock Prices for", symbol),
     xlab = "Date", ylab = "Price")
lines(stock_data_df$Close ~ stock_data_df$Date, type = "l", col = "red")
lines(stock_data_df$Adjusted ~ stock_data_df$Date, type = "l", col = "green")
lines(stock_data_df$High ~ stock_data_df$Date, type = "l", col = "orange")
lines(stock_data_df$Low ~ stock_data_df$Date, type = "l", col = "purple")

# 添加图例，此时可正常显示
legend("topright",
       legend = c("Opening Prices", "Closing Prices", "Adjusted Prices", "High Prices", "Low Prices"),
       lty = 1,
       col = c("blue", "red", "green", "orange", "purple"))

内容的提问来源于stack exchange，提问作者Mohammad Mustak Absar Khan