找到R中最大值的索引 [英] finding the index of a max value in R

问题描述

我有以下数据框架称为喘振：

I have the following data frame called surge:

MeshID    StormID Rate Surge Wind
1         1412 1.0000E-01   0.01 0.0
2         1412 1.0000E-01   0.03 0.0
3         1412 1.0000E-01   0.09 0.0
4         1412 1.0000E-01   0.12 0.0
5         1412 1.0000E-01   0.02 0.0
6         1412 1.0000E-01   0.02 0.0
7         1412 1.0000E-01   0.07 0.0
1         1413 1.0000E-01   0.06 0.0
2         1413 1.0000E-01   0.02 0.0
3         1413 1.0000E-01   0.05 0.0

我使用以下代码来查找每个风暴潮的最大值：

I used the following code to find the max value of surge per storm:

MaxSurge <- data.frame(tapply(surge[,4], surge[,2], max))

它返回： / p>

It returns:

1412 0.12
1413 0.06

这是非常好的，除了我也希望在浪潮最大的地方包含 MeshID 值。我知道我可以使用 which.max ，但我不清楚如何把它放在行动中。我非常喜欢R编程。

This is great, except I'd also like it to include the MeshID value at the point where the surge is the maximum. I know I can probably use which.max, but I can't quite figure out how to put this in action. I'm VERY new to R programming.

推荐答案

如果最多有2个data.points， which.max 只会引用第一个。一个更完整的解决方案将涉及排名：

If you have 2 data.points at the maximum, which.max will only refer to the first one. A more complete solution would involve rank:

# data with a tie for max  
surge <- data.frame(MeshID=c(1:7,1:4),StormID=c(rep(1412,7),
rep(1413,4)),Surge=c(0.01,0.03,0.09,0.12,0.02,0.02,0.07,0.06,0.02,0.05,0.06))

# compute ranks  
surge$rank <- ave(-surge$Surge,surge$StormID,FUN=function(x) rank(x,ties.method="min"))
# subset on the rank  
subset(surge,rank==1)
   MeshID StormID Surge rank
4       4    1412  0.12    1
8       1    1413  0.06    1
11      4    1413  0.06    1

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