合并矢量和data.frame匹配列值和矢量值

Question

I have

vetor <- c(1,2,3)
data <- data.frame(id=c('a', 'b', 'a', 'c', 'a'))

I need a data.frame output that match each vector value to a specific id, resulting:

  id vector1
1  a       1
2  b       2
3  a       1
4  c       3
5  a       1

Answer 1

Here are two approaches I often use for similar situations:

vetor <- c(1,2,3)
key <- data.frame(vetor=vetor, mat=c('a', 'b', 'c'))
data <- data.frame(id=c('a', 'b', 'a', 'c', 'a'))

data$vector1 <- key[match(data$id, key$mat), 'vetor']
#or with merge
merge(data, key, by.x = "id", by.y = "mat")

Answer 2

So you want one unique integer for each different id column?

This is called a factor in R, and your id column is one.

To convert to a numeric representation, use as.numeric :

data <- data.frame(id=c('a', 'b', 'a', 'c', 'a'))
data$vector1 <- as.numeric(data$id)

This works because data$id is not a column of strings, but a column of factors .

Answer 3

Here's an answer I found that follows the "mathematical.coffee" tip:

vector1 <- c('b','a','a','c','a','a')  # 3 elements to be labeled: a, b and c
labels <- factor(vector1, labels= c('char a', 'char b', 'char c') )
data.frame(vector1, labels)

The only thing we need to observe is that in the factor(vector1,...) function, vector1 will be ordered and the labels must follow that order correctly.