# 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:

  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:

[]
 “Mazda RX4” “Mazda RX4 Wag” “Datsun 710” “Hornet 4 Drive”
 “Hornet Sportabout” “Valiant” “Duster 360” “Merc 240D”
 “Merc 230” “Merc 280” “Merc 280C” “Merc 450SE”
 “Merc 450SL” “Merc 450SLC” “Cadillac Fleetwood” “Lincoln Continental”
 “Chrysler Imperial” “Fiat 128” “Honda Civic” “Toyota Corolla”
 “Toyota Corona” “Dodge Challenger” “AMC Javelin” “Camaro Z28”
 “Pontiac Firebird” “Fiat X1-9” “Porsche 914-2” “Lotus Europa”
 “Ford Pantera L” “Ferrari Dino” “Maserati Bora” “Volvo 142E”
[]
 “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