firstDayMonth.R

## --------------------------- ##
## Function takes a vector of  ##
## dates as its input.         ##
##                             ##
## It produces a vector of     ##
## dates that are the first    ##
## in their respective months  ##
## --------------------------- ##

firstDayMonth=function(x)
{           
     x=as.Date(as.character(x))
     day = format(x,format="%d")
     monthYr = format(x,format="%Y-%m")
     y = tapply(day,monthYr, min)
     first=as.Date(paste(row.names(y),y,sep="-"))
     as.factor(first)
}