R：用data.table中另一列中的字符串替换一列中的部分字符串答案

【问题标题】：R: Replace part of the string in one column with a string in another column in data.tableR：用data.table中另一列中的字符串替换一列中的部分字符串
【发布时间】：2023-03-20 05:08:01
【问题描述】：

我有以下两列 data.table；

library(data.table)
dt1 <- as.data.table(data.frame(
    relative.1 = c("up", "down", "up", "down", "down", 
      "up", "up", "up", "down", "down"), 
    color.1 = c(
        "<span style=     color: red !important; >0.00239377213823793</span>", 
        "<span style=     color: red !important; >0.0189475913373258</span>", 
        "<span style=     color: red !important; >0.000944874682014027</span>", 
        "<span style=     color: red !important; >0.00115563834695583</span>", 
        "<span style=     color: red !important; >0.00190146895689528</span>", 
        "<span style=     color: red !important; >0.00905363339565874</span>", 
        "<span style=     color: red !important; >0.00786719465124788</span>", 
        "<span style=     color: red !important; >0.0021806607355806</span>", 
        "<span style=     color: black !important; >0.0677967189492317</span>", 
        "<span style=     color: black !important; >0.0643565809998716</span>"
    ), stringsAsFactors = FALSE))

我想将“>”和“

如果有任何指点，我将不胜感激。

【问题讨论】：

标签： r replace data.table

【解决方案1】：

data.table 包使用更新就地操作符:= 让您能够有效地更新列。您可以参考 data.table 范围内的其他列。有多种方法可以对字符串进行编辑，虽然正则表达式是 not suitable for parsing HTML，但以下模式适用于您在此处的示例。

dt1[, color.1 := stringr::str_replace(
    string = color.1, 
    pattern = "[0-9.]+", 
    replacement = relative.1)]
dt1
# relative.1                                                color.1
#  1:         up     <span style=     color: red !important; >up</span>
#  2:       down   <span style=     color: red !important; >down</span>
#  3:         up     <span style=     color: red !important; >up</span>
#  4:       down   <span style=     color: red !important; >down</span>
#  5:       down   <span style=     color: red !important; >down</span>
#  6:         up     <span style=     color: red !important; >up</span>
#  7:         up     <span style=     color: red !important; >up</span>
#  8:         up     <span style=     color: red !important; >up</span>
#  9:       down <span style=     color: black !important; >down</span>
# 10:       down <span style=     color: black !important; >down</span>

【讨论】：

关于“pattern = "[0-9.]+"" 的一个快速问题。您能解释一下在这种情况下“[0-9.]+”如何只选择数字字符吗？谢谢。
如果你看一下?regex，就会有正则表达式的入门知识。它们是深入而强大的工具，但xkcd.com/1171。 [] 表示一组可供选择的值。 0-9 表示 0 到 9 范围内的所有值。+ 表示其中 1 个或多个一起，中间没有任何其他字符。

【解决方案2】：

dt1[, color.1 := sub('(?<=>)[0-9]+\\.[0-9]+(?=<)', relative.1, color.1, perl = TRUE), by = relative.1]

#     relative.1                                                color.1
#  1:         up     <span style=     color: red !important; >up</span>
#  2:       down   <span style=     color: red !important; >down</span>
#  3:         up     <span style=     color: red !important; >up</span>
#  4:       down   <span style=     color: red !important; >down</span>
#  5:       down   <span style=     color: red !important; >down</span>
#  6:         up     <span style=     color: red !important; >up</span>
#  7:         up     <span style=     color: red !important; >up</span>
#  8:         up     <span style=     color: red !important; >up</span>
#  9:       down <span style=     color: black !important; >down</span>
# 10:       down <span style=     color: black !important; >down</span>

【讨论】：