Working with matrices

Question 1

Assign name attributes to rows of a matrix

Answer 1

rownames(matrix)

Question 2

Assign name attributes to columns of a matrix

Answer 2

colnames(matrix)

Question 3

Finding matrix dimensions

Answer 3

dim(math_chemistry)

Question 4

Combining vectors or matrices by row

Answer 4

rbind(matrix_1, matrix_2)
rbind(vector_1, vector_2)
rbind(vector_1, matrix_1)

Question 5

Combining vectors or matrices by column

Answer 5

cbind(matrix_1, matrix_2)
cbind(vector_1, vector_2)
cbind(vector_1, matrix_1)

Question 6

Extract a single element

Answer 6

matrix[2, 5]

matrix[“row”, “column”]

Question 7

Extract multiple elements

Answer 7

matrix[c(1, 2), c(1, 3)]

matrix[c(“Harvard”, “Stanford”), c(“world_rank, “influence”)]

Question 8

Extract a single row

Answer 8

matrix[1, ]

matrix[“Harvard”, ]

Question 9

Extract a single column

Answer 9

matrix[ , 2]

matrix[ , “quality_of_education”]

Question 10

Extract multiple rows or columns

Answer 10

matrix[c(2, 4, 5), ]

matrix[ , c(“quality”, “influence”, impact”)]

Question 11

Sum of values in a matrix

Answer 11

sum(matrix[ , “column_name”])

sum(matrix[“row_name”, ])