Question

我正在尝试创建一个包含n列的数据框（df1）（在本例中为3）。第1列应该是数据帧df0中的随机列。第2列应该是相同随机列的平均值加上来自df0的其他四个随机列。第3列应该是前五个加上另外五个随机列的平均值。

Answer 1

我试着逐一回答你的问题。让我们从第一个开始

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

为了删除所有不需要的列，我个人使用如下所示的内容但我相信还有另一种方法可以做到这一点

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

找到平均值

1 个答案: