Namings

By this time, we referred to matrix elements by indices. But in the case of large matrices, it will be quite hard to remember and find where precisely necessary elements are.

This issue can be solved by using names on rows/columns. To set names (stored in names vector) of rows for matrix m use rownames(m) <- names. To set names of columns use the same syntax: colnames(m) <- names.

Note

Note that the length of vector names must equal the number of rows or columns respectively. For example, you can not assign 3 column names to a matrix with 4 columns.

For example, let's assign some names to the example matrix.


              12345678910
            
# Vector of integers
num <- 1:9
# Matrix
m <- matrix(num, nrow = 3, ncol = 3, byrow = T)

# Assign names of rows
rownames(m) <- c('r1', 'r2', 'r3')
# Assign names of columns
colnames(m) <- c('c1', 'c2', 'c3')
m # Output the matrix

As you can see, there are names on both rows and columns. If you have names on rows and (or) columns, you can refer to a specific element(s) by using names. You can do it the same way as indexing: specify the name/names of row(s)/column(s) to extract. For example, from the matrix above, we can extract the element 4 (r2 and c1) and the first row (r1).


              12345678
            
num <- 1:9
m <- matrix(num, nrow = 3, ncol = 3, byrow = T)
rownames(m) <- c('r1', 'r2', 'r3')
colnames(m) <- c('c1', 'c2', 'c3')
# Extact element `4` using namings
m["r2", "c1"]
# Extract the first row
m["r1",]

Tarefa

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Remember the task with a local furniture store? Assume we have 3 months of selling data.

Month	Sofa	Armchair	Dining table	Dining chair	Bookshelf
March	16	21	30	23	10
April	40	39	13	21	16
May	11	21	36	32	16

This data is stored in the sellings variable without row and column names. Your tasks are:

Assign c("March", "April", "May") to row names of sellings.
Assign c("Sofa", "Armchair, "Dining_table", "Dining_chair", "Bookshelf") to column names (pay attention to underscore _ characters!).
Output matrix sellings.

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Seção 1. Capítulo 5

Namings

By this time, we referred to matrix elements by indices. But in the case of large matrices, it will be quite hard to remember and find where precisely necessary elements are.

Note

Note that the length of vector names must equal the number of rows or columns respectively. For example, you can not assign 3 column names to a matrix with 4 columns.

For example, let's assign some names to the example matrix.


              12345678910
            
# Vector of integers
num <- 1:9
# Matrix
m <- matrix(num, nrow = 3, ncol = 3, byrow = T)

# Assign names of rows
rownames(m) <- c('r1', 'r2', 'r3')
# Assign names of columns
colnames(m) <- c('c1', 'c2', 'c3')
m # Output the matrix


              12345678
            
num <- 1:9
m <- matrix(num, nrow = 3, ncol = 3, byrow = T)
rownames(m) <- c('r1', 'r2', 'r3')
colnames(m) <- c('c1', 'c2', 'c3')
# Extact element `4` using namings
m["r2", "c1"]
# Extract the first row
m["r1",]

Tarefa

Swipe to show code editor

Remember the task with a local furniture store? Assume we have 3 months of selling data.

Month	Sofa	Armchair	Dining table	Dining chair	Bookshelf
March	16	21	30	23	10
April	40	39	13	21	16
May	11	21	36	32	16

This data is stored in the sellings variable without row and column names. Your tasks are:

Assign c("March", "April", "May") to row names of sellings.
Assign c("Sofa", "Armchair, "Dining_table", "Dining_chair", "Bookshelf") to column names (pay attention to underscore _ characters!).
Output matrix sellings.

Mude para o desktop para praticar no mundo realContinue de onde você está usando uma das opções abaixo

Tudo estava claro?

Obrigado pelo seu feedback!

Seção 1. Capítulo 5

Mude para o desktop para praticar no mundo realContinue de onde você está usando uma das opções abaixo