Lære Labeling Rows and Columns

Instead of referring to matrix elements by numeric indices, you can assign names to rows and columns. This makes large matrices easier to read and navigate.

Assigning Names

You can use rownames() and colnames() functions to add labels to rows and columns.

Example


              12345678
            
m <- matrix(1:9, nrow = 3, byrow = TRUE)

# Assign row names
rownames(m) <- c("r1", "r2", "r3")
# Assign column names
colnames(m) <- c("c1", "c2", "c3")

m

Note

The number of names must match the number of rows or columns in the matrix.

Accessing by Names

Once names are assigned, you can extract elements or entire rows/columns using them.

Example


              123456789
            
num <- 1:9
m <- matrix(num, nrow = 3, ncol = 3, byrow = T)
rownames(m) <- c('r1', 'r2', 'r3')
colnames(m) <- c('c1', 'c2', 'c3')

# Extract element at row "r2", column "c1" (value 4)
m["r2", "c1"]
# Extract the entire first row
m["r1",]

Using names instead of indices makes code more readable and less error-prone.

Opgave

Swipe to start coding

You are given a matrix sellings that stores sales data for a local furniture store across three months:

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

The matrix currently lacks row and column names.

Your tasks are to:

Assign c("March", "April", "May") to row names of sellings.
Assign c("Sofa", "Armchair, "Dining_table", "Dining_chair", "Bookshelf") to column names. Pay attention: use underscore (_) characters instead of spaces.
Output matrix sellings.

Løsning

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Sektion 1. Kapitel 31

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Instead of referring to matrix elements by numeric indices, you can assign names to rows and columns. This makes large matrices easier to read and navigate.

Assigning Names

You can use rownames() and colnames() functions to add labels to rows and columns.

Example


              12345678
            
m <- matrix(1:9, nrow = 3, byrow = TRUE)

# Assign row names
rownames(m) <- c("r1", "r2", "r3")
# Assign column names
colnames(m) <- c("c1", "c2", "c3")

m

Note

The number of names must match the number of rows or columns in the matrix.

Accessing by Names

Once names are assigned, you can extract elements or entire rows/columns using them.

Example


              123456789
            
num <- 1:9
m <- matrix(num, nrow = 3, ncol = 3, byrow = T)
rownames(m) <- c('r1', 'r2', 'r3')
colnames(m) <- c('c1', 'c2', 'c3')

# Extract element at row "r2", column "c1" (value 4)
m["r2", "c1"]
# Extract the entire first row
m["r1",]

Using names instead of indices makes code more readable and less error-prone.

Opgave

Swipe to start coding

You are given a matrix sellings that stores sales data for a local furniture store across three months:

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

The matrix currently lacks row and column names.

Your tasks are to:

Assign c("March", "April", "May") to row names of sellings.
Assign c("Sofa", "Armchair, "Dining_table", "Dining_chair", "Bookshelf") to column names. Pay attention: use underscore (_) characters instead of spaces.
Output matrix sellings.

Løsning

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Sektion 1. Kapitel 31

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