r - How can I obtain the colnames from part of a sorted matrix column? -
i have following in r:
> require("pls") > set.seed(42) > = matrix(rnorm(12), ncol=4) > [,1] [,2] [,3] [,4] [1,] 1.3709584 0.6328626 1.51152200 -0.0627141 [2,] -0.5646982 0.4042683 -0.09465904 1.3048697 [3,] 0.3631284 -0.1061245 2.01842371 2.2866454 > b <- c(1, 2, 3) > mymodel <- pcr(b ~ a) > mymodel$loadings loadings: comp 1 comp 2 a1 0.654 0.165 a2 0.136 -0.255 a3 0.415 0.732 a4 -0.618 0.609 > comp1 <- mymodel$loadings[, 1] > comp1 a1 a2 a3 a4 0.6539036 0.1362937 0.4146222 -0.6179988 > sort(comp1, decreasing=true) a1 a3 a2 a4 0.6539036 0.4146222 0.1362937 -0.6179988 > sort(comp1, decreasing=true)[1] a1 0.6539036 i puzzled comp1 is:
> colnames(comp1) null > rownames(comp1) null > dim(comp1) null > str(comp1) named num [1:4] 0.654 0.136 0.415 -0.618 - attr(*, "names")= chr [1:4] "a1" "a2" "a3" "a4" > typeof(comp1) [1] "double" questions:
- what data structure comp1?
- what should obtain column names sorted comp1
"a1", "a3", "a2", "a4"?
a question in lots of ways, since these small important distinctions vex many new , intermediate r users. in case call pcr returned list called mymodel. question showed use str() method examine return objects, , best place start. can consult page ?pcr explains return list of named components plus "all components returned underlying fit function". pcr(), underlying fit function svdpc.fit, , page function details remaining items in my model list.
as can see below, mymodel$loadings numeric vector 2 named dimensions (through list dimnames), known matrix. use of [ operator slice out first column (in code, named "comp 1" since both more clear , less break should column order ever change) returns simple numeric vector because have chosen single column matrix. can tell not matrix because has no dimensions, length.
> str(mymodel$loadings) loadings [1:4, 1:2] 0.654 0.136 0.415 -0.618 0.165 ... - attr(*, "dimnames")=list of 2 ..$ : chr [1:4] "a1" "a2" "a3" "a4" ..$ : chr [1:2] "comp 1" "comp 2" > is.matrix(mymodel$loadings) [1] true > str(mymodel$loadings[, "comp 1"]) named num [1:4] 0.654 0.136 0.415 -0.618 - attr(*, "names")= chr [1:4] "a1" "a2" "a3" "a4" > dim(mymodel$loadings[, "comp 1"]) null the way r drops dimensions when extract single-column slice not behaviour prefer, if want write general code returns same object type. 1 way around this, colnames() would work you, use drop = false argument in [. (see ?"[") keeps matrix dimensions , dimnames:
> altslice <- mymodel$loadings[, "comp 1", drop = false] > colnames(altslice) [1] "comp 1" > dim(altslice) [1] 4 1 > is.matrix(altslice) [1] true 
Comments
Post a Comment