'min'对因素没有意义

Question

Exchange_rate <-read.csv("Exchange.csv")

str(Exchange_rate)

summary(Exchange_rate)
weekdays = data.frame(wdy =c("Thu","Fri","Mon","Tue","Wed"),x =runif(5),y =runif(5))

summary(Exchange_rate$forecast)

library(ggplot2)
library(reshape2)
library(gridExtra)

min(as.character(as.numeric(Exchange_rate$YYYYMMDD)), na.rm=TRUE)

normalize<-function(x){return((x-min(x))/(max(x)-min(x)))}

exchangeN<-as.data.frame(lapply(Exchange_rate, normalize)) //ERROR AT THIS LINE

summary(exchangeN)

我得到以下错误

exchangeN <-as.data.frame（lapply（Exchange_rate，normalize））Summary.factor中的错误（c（115L，117L，120L，122L，124L，125L，126L，130L，：'min'对因子无意义

为什么我得到这个，我该如何解决这个问题？

Answer 1

lapply(Exchange_rate, normalize)与lapply(as.list(Exchange_rate), normalize)相同;它将normalize应用于每一列。其中一列是一个因素。 str应该告诉你哪一个。