r - 如何仅针对 R 中的一组记录更改一列的值

Question

有没有一种直接的方法可以根据 Y 列的值将 X 列中的值更改为 NA？

我有一个包含多个雷达数据的大型数据框。我只想将radarID“CLX”（Y列）的X列值（密度）更改为NA。

在 Excel 中，这将是一个简单的选择所有具有radarID =“CLX”的行，并用NA 替换所有密度值。

谢谢

Answer 1

In R also it is too simple, specially if you give us a reproducible example.

Here I create one :

dat <- data.frame( radarID = sample(c("CLX","OTHER"),10,rep=TRUE),
            X = rnorm(10))

Then using transform and ifelse, you can do something like this :

transform(dat,X=ifelse(radarID=='CLX',NA,X))

  radarID           X
1    OTHER -1.03632461
2    OTHER  0.07634564
3    OTHER -0.33788092
4      CLX          NA
5      CLX          NA
6      CLX          NA
7    OTHER  1.37040083
8    OTHER  0.50905176
9      CLX          NA
10   OTHER -0.16086215

Of course this will work in a copy of your data. You need to assign it assign to dat if you want to have the change.

dat <- transform(dat,X=ifelse(radarID=='CLX',NA,X))

Answer 2

One way to do it is as follows. If df is your data frame with two columsn x and y and you want to change x based on y such that when y is less than 10, x should become NA:

df[df$y < 10, 'x'] <- NA

You could also check out ?transform and ?within

Answer 3

df = data.frame(Density = 1:4, radarID = c("blah", "boo", "CLX", "bam"))
df$Density[df$radarID == "CLX"] = NA