在两个步骤中，您可以重新排列列：

  dat $ C<  -  NA 
 dat  ACB 
 1 0.596068 NA -0.7783724 
 2 -1.464656 NA -0.8425972 
 

你也可以使用 append

  dat<  -  data.frame = rnorm（2），B = rnorm（2））
 as.data.frame（append（dat，list（C = NA），after = 1））

 ACB 
 1 -0.7046408 NA 0.2117638 
 2 0.8402680 NA -2.0109721 
 

I want to add a new column with "NA"s in my dataframe:

     A       B
1    14379  32094
2   151884  174367
3   438422  449382

But I need it to be located between col. A and B, like this:

     A       C      B
1    14379   NA    32094
2   151884   NA    174367
3   438422   NA    449382

I know how to add col. C after col. B, but that is not helpful to me... Anyone know how to do it? Thanks!!!

In 2 steps, you can reorder the columns:

dat$C <- NA
dat <- dat[, c("A", "C", "B")]
         A  C          B
1  0.596068 NA -0.7783724
2 -1.464656 NA -0.8425972

You can also use append

dat <- data.frame(A = rnorm(2), B = rnorm(2))
as.data.frame(append(dat, list(C = NA), after = 1))

           A   C          B
1 -0.7046408  NA  0.2117638
2  0.8402680  NA -2.0109721