Hi,
Try:
set.seed(49)
mat1<-
matrix(sample(0:1,15*100,replace=TRUE),nrow=15,ncol=100,dimnames=list(LETTERS[1:15],paste0("D",sprintf("%04d",1:100))))
rowSums(mat1[rownames(mat1)%in% c("A","D","L"),])
# A D L
#44 55 50
A.K.
----- Original Message -----
From: Elaine Kuo <elaine.kuo...@gmail.com>
To: "r-help@r-project.org" <r-help@r-project.org>
Cc:
Sent: Tuesday, October 8, 2013 7:21 AM
Subject: [R] row sum with all absence in a presence-absence matrix
Dear list
I have a matrix composed of islandID as rows and speciesID as columns.
IslandID: Island A, B, C….O (15 islands in total)
SpeciesID: D0001, D0002, D0003….D0100 (100 species in total)
The cell of the matrix describes presence (1) or absence (0) of the species
in an island.
Now I would like to search how many species are found in (1, presence) for
Island A, Island D, and Island L respectively.
Please kindly advise the R code for the search purpose.
Thank you.
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and provide commented, minimal, self-contained, reproducible code.
