In my code, I want to extract the last largest value across a range of columns, iterating row-wise over the data frame. The problem is that my script only gives me the first occurrence (name of the first column in this case) that has the maximum value. Any suggestions on how I can update this line to get the last maximum value?

My data frame looks like this:

A.trust B.trust C.trust D.trust E.trust F.trust G.trust H.trust I.trust J.trust K.trust L.trust M.trust
-999    -999    -999    -999    -999    -999    -999.0  -999.0  -999.0   -999   -999    -999    -999
-999    -999    -999    -999    -999    -999     0.5    -999.0   0.5     -999   -999    -999    -999
-999    -999    -999    -999    -999    -999    -999.0  -999.0   1.0     -999   -999    -999    -999
-999    -999    -999    -999    -999    -999    -999.0  -999.0  -999.0   -999   -999    -999    -999
-999    -999    -999    -999    -999    -999    -999.0  -999.0  -999.0   -999   -999    -999    -999
-999    -999    -999    -999    -999    -999     0.5     0.5    -999.0   -999   -999    -999    -999

I am using the following code

# return cols which hold maximum
nams <- names(test)[apply(test, 1 ,which.max)]

Current Output

Currently, the value in the nams variable is:

"A.trust"
"G.trust" 
"I.trust" 
"A.trust"
"A.trust" 
"G.trust"

Required Output

My required value in the nams variable is this:

"M.trust" 
"I.trust" 
"I.trust"
"M.trust" 
"M.trust" 
"H.trust"

dput()

test = structure(list(A.trust = c(-999, -999, -999, -999, -999, -999), 
               B.trust = c(-999, -999, -999, -999, -999, -999), 
               C.trust = c(-999, -999, -999, -999, -999, -999), 
               D.trust = c(-999, -999, -999, -999, -999, -999), 
               E.trust = c(-999, -999, -999, -999, -999, -999), 
               F.trust = c(-999, -999, -999, -999, -999, -999), 
               G.trust = c(-999,  0.5, -999, -999, -999,  0.5), 
               H.trust = c(-999, -999, -999, -999, -999,  0.5), 
               I.trust = c(-999,  0.5,  1,   -999, -999, -999), 
               J.trust = c(-999, -999, -999, -999, -999, -999), 
               K.trust = c(-999, -999, -999, -999, -999, -999), 
               L.trust = c(-999, -999, -999, -999, -999, -999), 
               M.trust = c(-999, -999, -999, -999, -999, -999)), 
          row.names = 600:605, class = "data.frame")

Related Posts

The following post is relevant to my problem but I am struggling with how to make this change in my script How to find the last occurrence of a certain observation in grouped data in R?. This is another related post which.max ties method in R. Any help would be greatly appreciated!

CodePudding user response：

names(rev(test))[apply(rev(test), 1, which.max)]
[1] "M.trust" "I.trust" "I.trust" "M.trust" "M.trust" "H.trust"

CodePudding user response：

Another possibility (probably less efficient than @Skaqqs's answer):

names(test)[apply(test, 1, function(x) tail(x == max(x), 1)]

CodePudding user response：

We may use vectorized option

 names(test)[ncol(test):1][max.col(rev(test), "first")]
[1] "M.trust" "I.trust" "I.trust" "M.trust" "M.trust" "H.trust"