为什么format()将数值变量转换为字符变量？

Question

我正在为一个简单的方差分析演示构建一个示例，如果不将数字向量转换为“字符”向量，似乎无法设置小数长度，有解决方案吗？

# use fGarch for building somewhat messy data
library(fGarch)
N = 30
set.seed(1976)
control = rsnorm(N, 25, 5, 1.8)
treatOne = rnorm(N, 25, 4)
treatTwo = rsnorm(N, 22, 5, -1.3)
treatThree = rsnorm(N, 20, 5, -1)

# bind groups into a single dataframe
mysteryOne = data.frame(control, treatOne, treatTwo, treatThree)
# "stack" the dataframe to combine it into one column
mysteryOne = stack(mysteryOne)
# rename the columns
library(plyr)
mysteryOne = rename(mysteryOne, c("values" = "anxiety", "ind" = "condition"))
# replace the experimental "condition" values with a "group code" 
mysteryOne$condition = c(rep(0, N), rep(1, N), rep(2, N), rep(3, N))

# specify vector types
mysteryOne[, 1] = as.numeric(mysteryOne[, 1])
mysteryOne[, 2] = as.factor(mysteryOne[, 2])

# restrict the numeric vector to two decimal points
mysteryOne[, 1] = format(round(mysteryOne[, 1], 2), nsmall = 2)

str(mysteryOne)

Answer 1

如果你真的想扔掉这些信息，你可以转一转：

head(round(mysteryOne[, 1], 2))
# [1] 19.99 26.39 30.39 20.31 21.32 23.22

美观的打印是一个文本格式问题。所以解决方案会给你字符串：

head(format(mysteryOne[, 1], nsmall = 2L, digits = 2))
# [1] "19.99" "26.39" "30.39" "20.31" "21.32" "23.22"

格式化输出，然后将其强制返回到数字，这几乎肯定不是您想要的。