Replacing values in a column where there is a match

Question

I\'m new to R programming and I\'m stuck on the example below.

Basically I have two data sets:

dataset1:

ID       Category        
1        CatZ         


        

Answer 1

A base R approach that uses match

df1$Category[match(df2$ID, df1$ID)] <- df2$Category
df1
#  ID Category
#1  1   Cat600
#2  2    CatVV
#3  3   Cat611
#4  4    CatQQ

data

df1 <- structure(list(ID = 1:4, Category = c("CatZZ", "CatVV", "CatAA", 
"CatQQ")), .Names = c("ID", "Category"), class = "data.frame", row.names = c(NA, 
-4L))

df2 <- structure(list(ID = c(1L, 3L), Category = c("Cat600", "Cat611"
)), .Names = c("ID", "Category"), class = "data.frame", row.names = c(NA, 
-2L))