nrow ncol dim and dimnames function in R

nrow in R:

nrow in R returns the number of rows of a data frame or matrix. Let’s use the mtcars data frame to demonstrate nrow function in R

# number of rows of a data frame - nrow  function in R

nrow(mtcars)

so the output will be

32

 

ncol in R:

ncol in R returns the number of columns of a data frame or matrix. Let’s use the mtcars data frame to demonstrate ncol function in R

# number of columns of a data frame.

ncol(mtcars)

so the output will be

11

 

dim in R:

dim in R can be used to

  • Get the number of rows and number of columns of a data frame
  • Assign the number of rows and number of columns while creating the data frame.

Get the number of rows and columns in a data frame:

# number of rows and number of columns of a data frame in R.

dim(mtcars)

output:

[1]  32   11

 

 Assign the number of rows and columns to a matrix or data frame:

# Assign number of rows and number of columns of a matrix in R.

x <- 1:12
dim(x) <- c(3,4)
x

dim() function assigns the number of rows and number of columns of a matrix in above example.so the vector sequence from 1 to 12 is assigned in a 3 * 4 matrix

output:

       [,1] [,2] [,3] [,4]

[1,]    1    4    7   10

[2,]    2    5    8   11

[3,]    3    6    9   12

dimnames in R

dimnames in R can be used to

Get the row names and column names of a data frame:

# row names and column names of a data frame in R.

dimnames(mtcars)

the dimnames function in R returns the dimension names i.e row names and column names in the list format

output:

[[1]]
[1] “Mazda RX4” “Mazda RX4 Wag” “Datsun 710” “Hornet 4 Drive”
[5] “Hornet Sportabout” “Valiant” “Duster 360” “Merc 240D”
[9] “Merc 230” “Merc 280” “Merc 280C” “Merc 450SE”
[13] “Merc 450SL” “Merc 450SLC” “Cadillac Fleetwood” “Lincoln Continental”
[17] “Chrysler Imperial” “Fiat 128” “Honda Civic” “Toyota Corolla”
[21] “Toyota Corona” “Dodge Challenger” “AMC Javelin” “Camaro Z28”
[25] “Pontiac Firebird” “Fiat X1-9” “Porsche 914-2” “Lotus Europa”
[29] “Ford Pantera L” “Ferrari Dino” “Maserati Bora” “Volvo 142E”
[[2]]
[1] “mpg” “cyl” “disp” “hp” “drat” “wt” “qsec” “vs” “am” “gear” “carb”

 

 

Assign row names and column names to a matrix or data frame:

# Assign row names and column names to a matrix in R.

x <- 1:12
dim(x) <- c(3,4)
dimnames(x) <- list(c("x","y","z"),c("a","b","c","d"))
x

dimnames() function assigns the row names and column names to a matrix in above example.

 output:

     a   b   c    d

x   1   4   7   10

y   2   5   8   11

z   3   6   9   12

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