r - 我似乎找不到正确的方法来索引前一个向量的平均值

Question

我目前正在处理一个家庭作业问题，该问题要求我将先前向量的平均值索引到新向量中。在选择前一个向量的平均值时，教师希望我们只选择所述平均值的 +-2 的元素。请看下面的问题。

从 rnorm.vector 中，仅选择值在平均值±2 标准差内的元素。将此新向量分配给变量 rnorm.select.vector 并显示该向量。

我尝试使用 [] 和其他索引标准

// Normal distribution of 30 numbers with a mean of 25 and Standard Deviation of 2.5

rnorm.vector <- rnorm(30, mean = 25, sd = 2.5)

// logical vector 

rnorm.logical.vector <- (rnorm.vector >= 25)
rnorm.logical.vector

// +- 2.5 of standard Deviation

rnorm.select.vector <- 

我似乎无法在没有错误的情况下获得正确的结果

标签： rindexing

Answer 1

因为我非常喜欢猫，所以我尝试举一个小例子，说明如何使用逻辑向量从现有向量中选择所需的元素（可以是猫名、随机数等）

# i got a list of my cats name
my_cats_names <- c("Boby", "Tara", "Petzi", "Felix", "Mauzi", "Schnurrli")
# and a coresponding list with my cats weight
my_cats_weight <- c(8, 4, 7, 5, 4, 5)
# so Boby has 8kg, Tara 7 and so on

# During last night someone has stolen my ham, and im suspecting one of my cats to be the thief. 
# Since it was a big ham im pretty sure it needs a cat of at least 6kg to steal and eat it,
# so i want to select all my cats that are 6kg or more from my list. 

which_one_is_over_6_kg_logical_vector <- my_cats_weight >= 6
which_one_is_over_6_kg_logical_vector
# > which_one_is_over_6_kg_logical_vector
# [1]  TRUE FALSE  TRUE FALSE FALSE FALSE
# This result tells me, that the first one in the list is over 6kg, the second one not the 3rd one is over and so on

# Now i can use the logical vector to select only those elements from my list, that fullfill my constraint (beeing over 6kg)
my_cats_over_6kg <- my_cats_names[which_one_is_over_6_kg_logical_vector]
my_cats_over_6kg
# > my_cats_over_6kg
# [1] "Boby"  "Petzi"
# im pretty sure it was Boby or Petzi

# So by creating a logical vector we can select items from an existing vector if they fullfill our constraint

取而代之的是一个猫名向量，您得到一个数字向量，您可以计算其平均值和标准差。而不是选择超过 6 公斤的猫，您需要低于均值 (your_vector) - 2*sd(your_vector) 的数字和高于均值 (your_vector) + 2*sd(your_vector) 的数字。

我希望所有的猫都会有所帮助，而不是造成额外的混乱:)