根据另一列中的值汇总一列中的数据 [英] Aggregate data in one column based on values in another column

问题描述

我知道有一个简单的方法可以执行此操作...但是，我无法弄清楚。

I know there is an easy way to do this...but, I can't figure it out.

R脚本中有一个数据框看起来像这样：

I have a dataframe in my R script that looks something like this:

A      B    C
1.2    4    8
2.3    4    9
2.3    6    0
1.2    3    3
3.4    2    1 
1.2    5    1

请注意，A，B和C是列名。而且我正在尝试获取这样的变量：

Note that A, B, and C are column names. And I'm trying to get variables like this:

sum1 <- [the sum of all B values such that A is 1.2]
num1 <- [the number of times A is 1.2]

任何简单做到这一点的方法？
我基本上想得到一个看起来像这样的数据框：

Any easy way to do this? I basically want to end up with a data frame that looks like this:

    A     num     totalB
   1.2    3       12
   etc    etc     etc

其中 num是特定次数出现一个值， totalB是给定A值的B值之和。

Where "num" is the number of times that particular A value appeared, and "totalB" is the sum of the B values given the A value.

推荐答案

我会使用聚合来获取两个聚合，然后合并到一个数据框中：

I'd use aggregate to get the two aggregates and then merge them into a single data frame:

> df
    A B C
1 1.2 4 8
2 2.3 4 9
3 2.3 6 0
4 1.2 3 3
5 3.4 2 1
6 1.2 5 1

> num <- aggregate(B~A,df,length)
> names(num)[2] <- 'num'

> totalB <- aggregate(B~A,df,sum)
> names(totalB)[2] <- 'totalB'

> merge(num,totalB)
    A num totalB
1 1.2   3     12
2 2.3   2     10
3 3.4   1      2

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