查找平均值

Question

我试图用n列（在这种情况下是3）创建一个数据帧（df1）。列1应该是来自数据帧df0的随机列。第2列应该是同一个随机列加上df0中的另外四个随机列的平均值。第3列应该是前五个加上另外五个随机列的平均值。

Answer 1

我试着一一解答你的问题。让我们从第一

total <- 15 # Total number of columns in df0 
sample <- 10 # Total number of columns I'm extracting from df0 
values <- 4 # Number of rows 
random <- sample(total,sample,replace=FALSE) 
df0 <- data.frame(matrix(data = rexp(values*total, rate = total), nrow = values, ncol = total)) 

#At first I select 10 random columns from df0 
df1 <- df0[, sample(ncol(df0), sample)] 


#I would create an empty data frame 

df2 <- data.frame(matrix(, nrow =values , ncol = 3)) 


#then assign the first column of df1 to the output , 
df2$X1 <- df1[,1] 

#then you get the average of five first random selected to second column of df2 
df2$X2 <- rowMeans(subset(df1[1:5])) 

#finally the average of 10 columns to the third column of df2 
df2$X3 <- rowMeans(subset(df1[1:10])) 


> df2 
#   X1   X2   X3 
#1 0.18816542 0.12617238 0.08728368 
#2 0.09855574 0.07592763 0.06069351 
#3 0.12022571 0.06045562 0.07964574 
#4 0.00260806 0.06172300 0.06225859 

开始为了消除所有不需要的列，我个人使用类似下面 ，但我相信会有另一种方式来做到这一点

# for example you only want to keep column 3 and 5 then 
col_list = c("X3", "X5") 
dfm = df0[,col_list]