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

There are many ways to do this.

You could first pick which rows are in res:

team$names[res]

Then you can pick which ones have gender being "F":

team$names[res][  team$genders[res]=="F"   ]

Note that team$genders[res] picks out the genders corresponding to the rows in res, and then you filter to only accept those that are female.

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If you liked, you could do it the other way round:

team$names[  team$genders=="F" & (1:nrow(team) %in% res) ] 

Here team$genders=="F" is a logical vector of length nrow(team), being TRUE whenever the gender is "F" and FALSE otherwise.

The 1:nrow(team) generates row numbers, and 1:nrow(team) %in% res is TRUE if the row number is in res.

The & says "make sure that the gender is "F" AND the row number is in res".

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You could even do which(team$genders=="F") which returns a vector of row numbers for females, and then do:

team$names[ intersect(  which(team$genders=="F") , res ) ]

where the intersect picks row numbers that are present in both res and the females.

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And I'm sure people with think of more ways.