Question

我有这样的数据集

data <- data.frame(Time=as.Date(c("2007-01-31", "2007-02-28", "2007-03-31", 
        "2007-04-30", "2007-05-31"), format="%Y-%m-%d"), 
        a=c(104.8587, 104.5483, 104.0210, 105.7185, 104.9054), 
        b=c(95.4, 95.9, 95.6, 95.5, 95.8))


> data
    Time        a    b
1 2007-01-31 104.8587 95.4
2 2007-02-28 104.5483 95.9
3 2007-03-31 104.0210 95.6
4 2007-04-30 105.7185 95.5
5 2007-05-31 104.9054 95.8

使用

ddata <- data.frame(diff(as.matrix(data[,-1])))
ddata$Time <- data[-1,1]
ddata <- ddata[c(3, 1:2)]

采取差异。

> ddata
    Time       a    b
1 2007-02-28 -0.3104  0.5
2 2007-03-31 -0.5273 -0.3
3 2007-04-30  1.6975 -0.1
4 2007-05-31 -0.8131  0.3

然后我使用write.csv(ddata, file="ddata.csv", row.names=FALSE)将其保存到csv文件中。但是，如果我重新加载它，值会改变。

> ddata <- read.table(file="ddata.csv", dec=",", header=T, sep=",")
> ddata
    Time                  a                   b
1 2007-02-28 -0.310400000000001                 0.5
2 2007-03-31 -0.527299999999997  -0.300000000000011
3 2007-04-30   1.69750000000001 -0.0999999999999943
4 2007-05-31 -0.813100000000006   0.299999999999997

舍入值仍然相同，但write.csv命令添加了一些小数。发生什么事情了？

Answer 1

您的write.csv操作，按原样导出数据，但略微舍入。

如果将数字设置为20，您会看到您认为-0.3实际上是-0.300000000000011369。

options(digits = 20)
ddata
    Time                    a                     b
1 2007-02-28 -0.31040000000000134  0.500000000000000000
2 2007-03-31 -0.52729999999999677 -0.300000000000011369
3 2007-04-30  1.69750000000000512 -0.099999999999994316
4 2007-05-31 -0.81310000000000571  0.299999999999997158

write.csv保存了奇怪的值

1 个答案: