Subsetting matrices

Question

Considering following vector res and matrix team. the vector res represent indices, and I require to extract only those names whose index number is in vector res and gender=

Answer 1

This should work if your team is either a matrix or a data.frame:

# emulate your data
team <- data.frame(names=LETTERS, genders=rep(c("M","F"), 13))
res <- 10:26

team[intersect(res, which(team[,"genders"]=="F")), "names"]
#[1] J L N P R T V X Z
#Levels: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

# Try with a matrix instead of data.frame
team <- as.matrix(team)
team[intersect(res, which(team[,"genders"]=="F")), "names"]
#[1] "J" "L" "N" "P" "R" "T" "V" "X" "Z"

The basic idea is to get the indices of the "F" gender rows (using which) and then use the set operation intersect to AND it with your res indices. There are also union and setdiff variants that can be useful at times.