Legends on time series plots in R

How do I add legends to my plot below?

library(quantmod)
library(PerformanceAnalytics)
library(imputeTS)
library(PortfolioAnalytics)

tickers <- c("FB", "AAPL", "AMZN", "NFLX")
weights <- c(.25, .25, .25, .25)

portfolioPrices <- NULL
for (Ticker in tickers)
  portfolioPrices <- cbind(portfolioPrices,
                           getSymbols.yahoo(Ticker, from="2016-01-01", periodicity = "daily", auto.assign=FALSE)[,4])

plot(portfolioPrices, legend = tickers)

If you convert portfolioPrices to a dataframe then add each line separately you can add a legend.

The following code doesn't create the best looking plot/legend but you could improve it by playing about with the legend/plot arguments.

Also, the lines could be added using a loop rather than being hard-coded.

library(quantmod)
library(PerformanceAnalytics)
library(imputeTS)
library(PortfolioAnalytics)

tickers <- c("FB", "AAPL", "AMZN", "NFLX")
weights <- c(.25, .25, .25, .25)

portfolioPrices <- NULL
for (Ticker in tickers)
  portfolioPrices <- cbind(
    portfolioPrices,
    getSymbols.yahoo(
      Ticker,
      from = "2016-01-01",
      periodicity = "daily",
      auto.assign = FALSE
    )[, 4]
  )
portfolioPrices <- data.frame(portfolioPrices)


plot(
  x = as.Date(rownames(portfolioPrices)),
  portfolioPrices$FB.Close,
  col = "black",
  type = "l",
  ylim = c(min(portfolioPrices), max(portfolioPrices)),
  main = "Stocks",
  xlab = "Date",
  ylab = "Price"
)
lines(x = as.Date(rownames(portfolioPrices)),
      portfolioPrices$AAPL.Close,
      col = "blue")
lines(x = as.Date(rownames(portfolioPrices)),
      portfolioPrices$AMZN.Close,
      col = "green")
lines(x = as.Date(rownames(portfolioPrices)),
      portfolioPrices$NFLX.Close,
      col = "red")

legend(
  "topleft",
  legend = tickers,
  col = c("black", "blue", "green", "red"),
  cex = 0.5,
  lwd = 2
)