CODEWITHSUNDEEP
rmax
krazyglue5
krazyglue5

Reputation: 43

Creating New Column with Maximum Value

I've spent a good deal of time looking into this subject, but have not been able to find much. I would like a new column of data titled "Max Region", that gives the name of the column for which the maximum value occurs in each row.

df <- data.frame(Head=c(9, 6, 2, NA), Thorax=c(9, 2, NA, NA), Abdomen=c(NA, NA, 5, 5), Neck=c(4, 3, 5, 2))

#  Head Thorax Abdomen Neck
#    9      9      NA    4
#    6      2      NA    3
#    2     NA       5    5
#   NA     NA       5    2

So far, I've used:

df$MaxRegion <- names(df)[apply(df, 1, which.max)]

However, in the case of a tie, I would really like both columns to result (ie HeadThorax or AbdomenNeck), or just result with "NA". Is this possible with which.max? I've also looked into max.col, but it also doesn't seem to have this function. Thank you so much!

Upvotes: 1

Views: 75

Answers (2)

ThomasIsCoding
ThomasIsCoding

Reputation: 101099

Another base R option

df$MaxRegion <- mapply(
  subset,
  list(names(df)),
  asplit(df == do.call(pmax, c(df, na.rm = TRUE)), 1)
)

gives

> df
  Head Thorax Abdomen Neck     MaxRegion
1    9      9      NA    4  Head, Thorax
2    6      2      NA    3          Head
3    2     NA       5    5 Abdomen, Neck
4   NA     NA       5    2       Abdomen

Upvotes: 1

akrun
akrun

Reputation: 886948

Using the OP's code, if we need to get all the tied max element column names, use %in%(returns FALSE where there are NA) or == on the max, and paste the corresponding names

apply(df, 1, function(x) toString(names(x)[x %in% max(x, na.rm = TRUE)]))
#[1] "Head, Thorax"  "Head"          "Abdomen, Neck" "Abdomen"

NOTE: which.max returns only the first index of the max value

Upvotes: 0

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