检查并替换R数据框中的列值

Question

I have multiple files to read in using R. I iterate through the files in a loop, obtain dataframes and then try to change values of a particular column. Examples of the R dataframes are as follows:

df_A:

ID  ZN
1   0
2   1
3   1
4   0

df_B:

ID  ZN
1   2
2   1
3   1
4   2

As shown above, the column 'ZN' for some dataaframes may have 0's and 1's and others dataframes have have 1's and 2's. What I want is - as I'm iterating through the files, I want to make changes only in the dataframes with column ZN having 1's and 2's like this: 1 to 0 and 2 to 1. Dataframes with ZN values as 0's and 1's will be left unchaged.

my attempt did not work:

if(dataframe$ZN > 1){
    dataframe$ZN<-recode(dataframe$ZN,"1=0;2=1")
  }
  else{
  dataframe$ZN
  }

Any solutions please?

Answer 1

One approach might be to decrement the value of ZN by one if we detect a single value of 2 anywhere in the column:

if (max(df_A$ZN) == 2) {
    df_A$ZN = df_A$ZN - 1
}

Demo

Answer 2

If there are only two values ie 0 and 1, then

df_A$ZN <- (df_A$ZN==0) + 1
df_A$ZN
#[1] 2 1 1 2

---

Or using case_when for multiple values

library(dplyr)
df_A %>%
  mutate(ZN = case_when(ZN==0 ~2, TRUE ~ 1))