Lab 4 Activity Activity4 Lab4 Instructions

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Lab 4 - Activity

Oleksandr Savenkov

10/3/2018

1. Write a function that normalizes a vector (with two parameters) :

•vector to be normalized

•

parameter that allows normalize the vector in two ways: only centered with zero mean and also

standardize with mean zero and standard deviation 1

Example:

•input (1, 2, 3, 4)

•centered vector is

standardize(a, centered_only = TRUE)

## [1] -1.5 -0.5 0.5 1.5

•standardized is

standardize(a, centered_only = FALSE)

## [1] -1.1618950 -0.3872983 0.3872983 1.1618950

2. Modify previous function in order to handle missing values in a vector

standardize(c(1,2,3,4,NA))

## [1] NA NA NA NA NA

standardize(c(1,2,3,4,NA), na.rm = TRUE)

## [1] -1.1618950 -0.3872983 0.3872983 1.1618950 NA

2. Create a 4 by 4 matrix

## [,1] [,2] [,3] [,4]

## [1,] 1 5 9 13

## [2,] 2 6 10 14

## [3,] 3 7 11 15

## [4,] 4 8 12 16

Create a function to calculate sum of matrix elements without built-in function sum()

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