如何在R语言中将字符向量的数值格式化为两位小数？

给定混合数值型字符串和非数值字符串的字符向量：

x = c("0.857138", "1", "0.5", "not limiting", "0.1", "0.233333333333333", 
      "1", "0.333333333333333", "1", "1", "0.1", "0.65", "1", "1", 
      "0.6", "0.25", "1", "1", "0.25", "0.6", "1", "1", "0.6")

可以通过以下方式仅对数值型元素保留两位小数，非数值元素保持原样：

方法一：强制保留两位小数（含末尾零） #

使用ifelse结合sprintf实现格式化：

processed_x <- ifelse(!is.na(as.numeric(x)), sprintf("%.2f", as.numeric(x)), x)

运行后结果：

> processed_x
 [1] "0.86"        "1.00"        "0.50"        "not limiting" "0.10"       
 [6] "0.23"        "1.00"        "0.33"        "1.00"        "1.00"       
[11] "0.10"        "0.65"        "1.00"        "1.00"        "0.60"       
[16] "0.25"        "1.00"        "1.00"        "0.25"        "0.60"       
[21] "1.00"        "1.00"        "0.60"

方法二：保留两位小数但去除末尾无意义的零 #

如果希望整数或一位小数的数值不显示末尾零（比如"1"保持为"1"，"0.5"保持为"0.5"），可以用formatC：

processed_x <- ifelse(!is.na(as.numeric(x)), 
                      formatC(as.numeric(x), format = "f", digits = 2, drop0trailing = TRUE), 
                      x)

运行后结果：

> processed_x
 [1] "0.86"        "1"           "0.5"         "not limiting" "0.1"        
 [6] "0.23"        "1"           "0.33"        "1"           "1"          
[11] "0.1"         "0.65"        "1"           "1"           "0.6"        
[16] "0.25"        "1"           "1"           "0.25"        "0.6"        
[21] "1"           "1"           "0.6"

内容的提问来源于stack exchange，提问作者confusedindividual