Question

我一直得到这个错误：

 Error in eval(expr, envir, enclos) : 
 could not find function "aggregation.method"

示例：

#sample data
Date.Time<- seq(ISOdate(2000,1,1), by = "min" , length.out = 200)
rh <- as.data.table(cbind(Date.Time,rnorm(200),rnorm(200),rnorm(200)))
colnames(rh) <- c("Date.Time", "A", "B", "C")
rh$Date.time <- as.POSIXct( rh$Date.Time, origin = "1970-01-01" )

#Custom function
Custom.data.wrangle<-function(x, timeinterval, aggregation.method)
{
  require(data.table)

  x$Date.Time <- as.POSIXct(as.integer(as.numeric(x$Date.Time) / (60 * timeinterval)) * (60 * timeinterval),
                            origin = "1970-01-01" ,
                            tz = "GMT")# Rounddown POSIXct in a simple form.

  x<-melt(x, id= "Date.Time")

  x<-dcast(x, Date.Time~variable, fun.aggregate = aggregation.method, na.rm=TRUE)  #Restructure the table
  return(x)
}

rh<- Custom.data.wrangle(rh, 30, mean)

我尝试过引号组合，noquote，

fun.aggregate = get(aggregation.method)

一切都无济于事。请保存我的理智！

Answer 1

我不确定这是预期的行为还是错误，但以下似乎有效：

f <- function(agg.fun) {
    dcast(
        DT, 
        time ~ variable, 
        fun.aggregate = eval(substitute(agg.fun)),
        #               ^^^^^^^^^^^^^^^^^^^^^^^^^
        na.rm = TRUE
    )
}

f(mean)
#     time    weight
#  1:    0  41.06000
#  2:    2  49.22000
#  3:    4  59.95918
#  4:    6  74.30612
#  5:    8  91.24490
#  6:   10 107.83673
#  7:   12 129.24490
#  8:   14 143.81250
#  9:   16 168.08511
# 10:   18 190.19149
# 11:   20 209.71739
# 12:   21 218.68889

library(data.table)
DT <- melt(
    setnames(
        as.data.table(ChickWeight),
        names(ChickWeight), tolower(names(ChickWeight))
    ),
    id = 2:4
)

eval中的错误（expr，envir，enclos）：找不到函数

1 个答案: