#generate time sequence
time <- seq.Date(from = as.Date("2002/01/01",format = "%Y/%m/%d"), by = "week", length.out = 679)
tail(time)
#transfer time sequence to matrix
time=matrix(time,nrow = length(time),ncol = 1)

dim(time)

slope3_1=matrix(NA,nrow=679,ncol=439) #679weeks, 439firms  

for(i in 1:439){
  stock=read.csv(paste("E:/CDS_data/stock_1/stock.", i,".csv", sep=""),header=T,stringsAsFactors=F,fill=TRUE)
  stock=select(stock,firms,date,slope3)
  stock[,"date"]=as.Date(stock[,"date"],form="%Y-%m-%d")
  tseq=as.character(time)
  tseq=as.Date(time,form="%Y/%m/%d")
  for(j in 1:679){

    if(stock[j,"date"]>=tseq[length(tseq)]){
      slope3_1[length(tseq),i]=stock[j,"slope3"]
      next
    }

    for(k in 1:678){

      if((stock[j,"date"]>=tseq[k])&(stock[j,"date"]<tseq[k+1])){
        slope3_1[k,i]=stock[j,"slope3"]
        break
      }

    }


  }
}
Error in if (stock[j, "date"] >= tseq[length(tseq)]) { :
  missing value where TRUE/FALSE needed