问题
For instance given:
dim1 <- c("P","PO","C","T")
dim2 <- c("LL","RR","R","Y")
dim3 <- c("Jerry1", "Jerry2", "Jerry3")
Q <- array(1:48, c(4, 4, 3), dimnames = list(dim1, dim2, dim3))
I want to reference within this array, the matrix that has the max dim3 value at the (3rd row, 4th column) location.
Upon identifying that matrix, I want to return the column name which has the maximum value within the matrix's (3rd Row, 1st Column) to (3rd Row, 3rd Column) range.
So what I'd hope to happen is that Jerry3 gets referenced because the number 47 is stored in its 3rd row, 4th column, and then within Jerry3, I would want the maximum number in row 3 to get referenced which would be 43, and ultimately, what I need returned (the only value I need) is then the column name which would be "R".
That's what I need to know how to do, obtain get that "R" and assign it to a variable, i.e. "column_ref", such that column_ref <- "R".
Please Please Please help.
回答1:
This should do it - if I understand correctly:
Q <- array(1:48, c(4,4,3), dimnames=list(
c("P","PO","C","T"), c("LL","RR","R","Y"), c("Jerry1", "Jerry2", "Jerry3")))
column_ref <- names(which.max(Q[3,1:3, which.max(Q[3,4,])]))[1] # "R"
Some explanation:
which.max(Q[3,4,]) # return the index of the "Jerry3" slice (3)
which.max(Q[3,1:3, 3]) # returns the index of the "R" column (3)
...and then names returns the name of the index ("R").
回答2:
This post helped me to solve a data.frame general problem.
I have repeated measures for groups, G1 e G2.
> str(df)
'data.frame': 6 obs. of 15 variables:
$ G1 : num 0 0 2 2 8 8
$ G2 : logi FALSE TRUE FALSE TRUE FALSE TRUE
$ e.10.100 : num 26.41 -11.71 27.78 3.17 26.07 ...
$ e.10.250 : num 27.27 -12.79 29.16 3.19 26.91 ...
$ e.20.100 : num 29.96 -12.19 26.19 3.44 27.32 ...
$ e.20.100d: num 26.42 -13.16 28.26 4.18 25.43 ...
$ e.20.200 : num 24.244 -18.364 29.047 0.553 25.851 ...
$ e.20.50 : num 26.55 -13.28 29.65 4.34 27.26 ...
$ e.20.500 : num 27.94 -13.92 27.59 2.47 25.54 ...
$ e.20.500d: num 24.4 -15.63 26.78 4.86 25.39 ...
$ e.30.100d: num 26.543 -15.698 31.849 0.572 29.484 ...
$ e.30.250 : num 26.776 -16.532 28.961 0.813 25.407 ...
$ e.50.100 : num 25.995 -14.249 28.697 0.803 27.852 ...
$ e.50.100d: num 26.1 -12.7 27.1 2.5 27.4 ...
$ e.50.500 : num 28.78 -9.39 25.77 2.73 23.73 ..
I need to know which measure (column) has the best (max) result. And I need to disconsider grouping columns.
I ended up with this function
apply(df[colIni:colFim], 1, function(x) colnames(df)[which.max(x)+(colIni-1)]
#colIni: first column to consider; colFim: last column to consider
After having column name, another tiny function to get the max value
apply(dfm,1,function(x) x[x[1]])
And the function to solve similar problems, that return the column and the max value
mxCol=function(df, colIni, colFim){ #201609
if(missing(colIni)) colIni=1
if(missing(colFim)) colFim=ncol(df)
if(colIni>=colFim) { print('colIni>=ColFim'); return(NULL)}
dfm=cbind(mxCol=apply(df[colIni:colFim], 1, function(x) colnames(df)[which.max(x)+(colIni-1)])
,df)
dfm=cbind(mxVal=as.numeric(apply(dfm,1,function(x) x[x[1]]))
,dfm)
return(dfm)
}
In this case,
> mxCol(df,3)[1:11]
mxVal mxCol G1 G2 e.10.100 e.10.250 e.20.100 e.20.100d e.20.200 e.20.50 e.20.500
1 29.958 e.20.100 0 FALSE 26.408 27.268 29.958 26.418 24.244 26.553 27.942
2 -9.395 e.50.500 0 TRUE -11.708 -12.789 -12.189 -13.162 -18.364 -13.284 -13.923
3 31.849 e.30.100d 2 FALSE 27.782 29.158 26.190 28.257 29.047 29.650 27.586
4 4.862 e.20.500d 2 TRUE 3.175 3.190 3.439 4.182 0.553 4.337 2.467
5 29.484 e.30.100d 8 FALSE 26.069 26.909 27.319 25.430 25.851 27.262 25.535
6 -9.962 e.30.250 8 TRUE -11.362 -12.432 -15.960 -11.760 -12.832 -12.771 -12.810
来源：https://stackoverflow.com/questions/10290801/getting-column-name-which-holds-a-max-value-within-a-row-of-a-matrix-holding-a-s