每日一练 | Data Scientist & Business Analyst 面试题 158

大数据应用 · 公众号 · 大数据 · 2017-08-12 08:52

正文

从6月15日起，数据应用学院将与你一起温习数据科学（DS）和商业分析（BA）领域常见的面试问题。希望积极寻求相关领域工作的你每天关注我们的问题并且与我们一起思考，我们将会在第二天给出答案。

Day 58

DS Interview Questions

Describe the basic steps to do the PCA (Principal Components Analysis)

BA Interview Questions

R language:

Using the following variable:

x=cbind(c(1,2,3,4,9,7,4,3),c(3,1,2,5,3,6,5,3))

type a for() loop that calculate y=3 8 18 44 126 140 100 84, such that:

y[1]=x[1,1]*x[1,2]

y[2]=x[2,1]*sum(x[1:2,2])

y[3]=x[3,1]*sum(x[1:3,2])

y[8]=x[8,1]*sum(x[1:8,2])

欲知答案如何？请见下期分解！

Day 57 答案揭晓

DS Interview Questions

Talk about how K-D Tree improve the KNN.

The k-d tree is a binary tree in which every node is a k-dimensional point. Every non-leaf node can be thought of as implicitly generating a splitting hyperplane that divides the space into two parts, known as half-spaces. Points to the left of this hyperplane are represented by the left subtree of that node and points right of the hyperplane are represented by the right subtree. The hyperplane direction is chosen in the following way: every node in the tree is associated with one of the k-dimensions, with the hyperplane perpendicular to that dimension's axis.

Basically, K-D Tree divides the dataset into several regions, and this time when we calculate the distances of the query instance, instead we calculate its distances to all the other data points, we only calculate the distances to all the data which in the same region with the query instance, thus reduce the calculation time complexity.

BA Interview Questions

R language:

Using the following variable:

x=as.Date("10/11/2017","%d/%m/%Y")

# type a repeat () loop that increment x until x is equal to 31/12/2017.

repeat{

x=x+1

print(x)

if(x=="2017-12-31") break;

}