Question

我有一个像这样的小数据框：

a<-c("green","green","green","green","green","green","green","green","green","green")
b<-c("blue","red","blue","red","blue","red","blue","red","blue","red")
df<-data.frame(a,b)
df
       a    b
1  green blue
2  green  red
3  green blue
4  green  red
5  green blue
6  green  red
7  green blue
8  green  red
9  green blue
10 green  red

我想替换＆＃34;绿色＆＃34; by＆＃34; yellow＆＃34;其中b ==＆＃34;红色＆＃34;

我可以按df[b=="red",]选择这些行，但替换不起作用。我试过了：

> df[b=="red",]$a<-gsub("green","yellow",df[b=="red",])
Fehler in `$<-.data.frame`(`*tmp*`, "a", value = c("c(1, 1, 1, 1, 1)",  : 
  replacement has 2 rows, data has 5

或

> df$a[subset(df$a,df$b=="red")]<-"yellow"
Warnmeldung:
In `[<-.factor`(`*tmp*`, subset(df$a, df$b == "red"), value = c(NA,  :
  invalid factor level, NA generated
> df
       a    b
1   <NA> blue
2  green  red
3  green blue
4  green  red
5  green blue
6  green  red
7  green blue
8  green  red
9  green blue
10 green  red

和

> df[b=="red",]$a<-"yellow"
Warnmeldung:
In `[<-.factor`(`*tmp*`, iseq, value = c("yellow", "yellow", "yellow",  :
  invalid factor level, NA generated
> df
       a    b
1  green blue
2   <NA>  red
3  green blue
4   <NA>  red
5  green blue
6   <NA>  red
7  green blue
8   <NA>  red
9  green blue
10  <NA>  red

这对我的问题都不起作用。什么是最简单的解决方案？非常感谢，Treppenlift。

Answer 1

您可以使用哪种功能。有关示例，请参阅http://www.endmemo.com/program/R/which.php。

rem // Let us assume variable `RelPath` holds the user input:
for %%I in ("%RelPath%") do set "EXT=%%~xI"
rem // Check whether the extension is missing:
if not defined EXT (
    rem /* There is no extension, so let us assume the user input is a directory;
    rem    so let us append the default file name `test.js` in that case: */
    set "RelPath=%RelPath%\test.js"
)
rem // Continue with the `dir`/`findstr` approach from use case 1 here...

R：如何将条件列中的字符串替换为第二列？

1 个答案: