我有以下数据:
a <- c(1,1,1,1,2,2,2,2)
b <- c(2,4,6,8,2,3,4,1)
c <- factor(c("A","B","A","B","A","B","A","B"))
df <- data.frame(
sp=a,
length=b,
method=c)
我可以使用以下方法通过方法计算每个物种的样本数量:
n <- with(df,tapply(sp,method,function(x) count(x)))
我如何通过每个物种的方法获得平均长度?
答案 0 :(得分:12)
我个人会使用aggregate
:
aggregate(length ~ sp, data = df, FUN= "mean" )
# by species only
# sp length
#1 1 5.0
#2 2 2.5
aggregate(length ~ sp + method, data = df, FUN= "mean" )
# by species and method
# sp method length
#1 1 A 4
#2 2 A 3
#3 1 B 6
#4 2 B 2
您可能想要的所有内容:
aggregate(length ~ method, data = df, function(x) c(m = mean(x), counts = length(x)) )
# counts and mean for each method
# method length.m length.counts
#1 A 3.5 4.0
#2 B 4.0 4.0
答案 1 :(得分:5)
图书馆plyr非常适合这样的事情
library(plyr)
new.df <- ddply(df, c("method", "sp"), summarise,
mean.length=mean(length),
max.length=max(length),
n.obs=length(length))
给你
> new.df
method sp mean.length max.length n.obs
1 A 1 4 6 2
2 A 2 3 4 2
3 B 1 6 8 2
4 B 2 2 3 2