在值列表之后，我想对 r 中的数据框进行子集化，其中行包含某列中的值

Question

I have a data frame and want to extract the rows that the value coincide with a certain vector. In the df, there are no duplicate. I need the data frame to keep the order of the vector.

Name <- c("Jon", "Bill", "Maria", "Ben", "Tina")
Age <- c(23, 41, 32, 58, 26)

mydf <- data.frame(Name, Age)

myvector <- c(23, 26, 32, 26) 

My expected answer would be

"Jon", "Tina", "Maria", "Tina"

This is one of the things I've tried:

> df[df$Age == to_find,]$Name
Warning message:
In df$Age == to_find :
  longer object length is not a multiple of shorter object length

Also this next solution doesn't give me all the expected rows and still gives me an error message:

> subset(df, Age == to_find)
   Name Age
1   Jon  23
3 Maria  32
Warning message:
In Age == to_find :
  longer object length is not a multiple of shorter object length

Thank you for your help!

Answer 1

The for loop below returns your desired output. It is also based on the assumption that no two people in your original dataset will have the same age. If that is the case, it simply gets the name of the first person in your dataset who matches the age. For example, if 'myvector' is looking for people aged 34, and there are two people, Joseph and Brian aged 34 in mydf, the new 'names' vector will only get the name of the first person from the dataset who matches the age 34, regardless of how many times you look for 34.

Name <- c("Jon", "Bill", "Maria", "Ben", "Tina")
Age <- c(23, 41, 32, 58, 26)

mydf <- data.frame(Name, Age)

myvector <- c(23, 26, 32, 26)

names <- vector(mode="character", length=length(myvector))

for (i in 1:length(names)) {
  
  for (j in 1:length(mydf$Name)) {
    
    if(mydf$Age[j] == myvector[i]) {
      names[i] <- mydf$Name[j]
    }
  }
}