每日一练 | Data Scientist & Business Analyst & Leetcode 面试题 358

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DS Interview Question

What is A/B Testing?

BA Interview Question

R Programming: explain the usage of which() function in R language and name an example of that function

LeetCode Question

Merge Two Sorted Lists

Description:

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Input: 1->3->5->null 2->4->6->7->null

Output:1->2->3->4->5->6->7->null

DS Interview Question & Answer

What's difference between pca and kernel pca?

Answer:

* The standard PCA always finds linear principal components to represent the data in lower dimension. Sometime, we need non-linear principal components.If we apply standard PCA for the below data, it will fail to find good representative direction. Kernel PCA (KPCA) rectifies this limitation.

* Kernel PCA just performs PCA in a new space.

* It uses Kernel trick to find principal components in different space (Possibly High Dimensional Space).

* PCA finds new directions based on covariance matrix of original variables. It can extract maximum P (number of features) eigen values. KPCA finds new directions based on kernel matrix. It can extract n (number of observations) eigenvalues.

* PCA allow us to reconstruct pre-image using few eigenvectors from total P eigenvectors. It may not be possible in KPCA.

* The computational complexity for KPCA to extract principal components take more time compared to Standard PCA.

BA Interview Question & Answer

R Programing: imagine you have two columns in a dataframe, ‘Gender’ and ‘Loan_Status’, both are categorical variables. ‘Gender’ has ‘Male’,’Female’ and NA values, ‘Loan_Status’ with ‘Yes’ and ‘No’. Now, how do you use ‘dplyr’ package to calculate the percentage for male and female when Loan Status equals to ‘No’, remember to ignore NA values.

Sample Output: