pctchange <- function(v) {
    # Incremental percent change
    (v - c(v[1],v[-(length(v))])) / c(v[1],v[-(length(v))])
    }

# weighted harmonic mean

whmean <- function(v, w){  #, na.rm=FALSE){
    #v <- ifelse(na.rm==TRUE, v[!is.na(v)],v )
    #w <- ifelse(na.rm==TRUE, w[!is.na(w)],w )
    sum(as.numeric(w))/sum(as.numeric(w)/as.numeric(v))
}

#weighted mean
wmean <- function(v, w) { #, na.rm=FALSE){
    #v <- ifelse(na.rm==TRUE, v[!is.na(v)],v )
    #w <- ifelse(na.rm==TRUE, w[!is.na(w)],w )
    sum(as.numeric(w)*as.numeric(v))/sum(as.numeric(w))
}

# format as percentage
# syntax: >sapply(df[c(...list of columns...),], percentify, r=1)

percentify <- function(x, r=1, keep.zeros=FALSE, na.code=""){
     ifelse (as.numeric(x) != 0 | keep.zeros==TRUE,  paste( format(round ( as.numeric(x) * 100, r) , nsmall=r) , '%', sep='')
            ,
            na.code)
}