为什么data.frame列未在R中更改

Question

I have following data frame:

ddf
  vnum1     vnum2
1     1 0.6380312
2     1 0.1737218
3     1 0.3528707
4     1 0.8670922
5     1 0.6498109
> 
> 
> str(ddf)
'data.frame':   5 obs. of  2 variables:
 $ vnum1: num  1 1 1 1 1
 $ vnum2: num  0.638 0.174 0.353 0.867 0.65
> 

I want to change all values of vnum1 from 1 to 4.

Why following do not work:

> rbind(ddf, ddf[,1]=4)
Error: unexpected '=' in "rbind(ddf, ddf[,1]="

Following adds only one number and that too to both columns. It is obviously not working correctly.

> rbind(ddf, (ddf[,1]=4))
  vnum1     vnum2
1     1 0.6380312
2     1 0.1737218
3     1 0.3528707
4     1 0.8670922
5     1 0.6498109
6     4 4.0000000

Answer 1

There are two problems here.

1. The code doesn't work because = as you're using it in the argument list of a function is incorrect. In rbind , = is used to assign names to the arguments.

   To see this, try rbind(ddf, ddf[,1] <- 4) versus rbind(ddf, ddf[,1]=4)

   Also try rbind(ddf, X = 3) and look at the row names.

2. rbind is a row bind function. So when you call rbind(ddf, ddf[,1]=4) you are trying to add a new row filled with 4's to the bottom of ddf .

---

That said, to replace all the values in the first column with 4, you can just use ddf[,1]=4 , like you have in your rbind call, or you can also do

ddf$vnum1 <- 4L