library(survival)

sp500 <- read.table("021513423.csv",header=T,sep=",")
names(sp500) <- c("caldt","sp500")

nyse <- read.table("021513260.csv",header=T,sep=",")
names(nyse) <- c("caldt","nyse")

nasdaq <- read.table("021513101.csv",header=T,sep=",")
names(nasdaq) <- c("caldt","nasdaq")
nasdaq$nasdaq[nasdaq$nasdaq == -99] <- NA

index <- merge(x=sp500, y=nyse, by.x="caldt", by.y="caldt", all=TRUE)
index <- merge(x=index, y=nasdaq, by.x="caldt", by.y="caldt", all=TRUE)

rm(sp500, nyse, nasdaq)