CODEWITHSUNDEEP
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Aargo
Aargo

Reputation: 53

nrow returns null value for only one row in R

When I subset just one row of a matrix and pass that to nrow as nrow(x[1,]) or nrow(x[2,]) it returns a NULL value instead of 1.

However if I subset more than one row then nrow(x[1:2,]) returns 2 which is a correct value.

Need help on how to handle cases like nrow(x[i,]). Thanks in advance.

Upvotes: 0

Views: 2828

Answers (2)

mufi
mufi

Reputation: 11

You can also use drop = FALSE in subsetting the matrix, which provides R from dropping the matrix class:

(m <- matrix(1, 3, 3))
#>      [,1] [,2] [,3]
#> [1,]    1    1    1
#> [2,]    1    1    1
#> [3,]    1    1    1
class(m[1, ])
#> [1] "numeric"
class(m[1, , drop = FALSE])
#> [1] "matrix" "array"

Then nrow() returns the desired result:

nrow(m[1, , drop = FALSE])
#> [1] 1
nrow(m[2, , drop = FALSE])
#> [1] 1

Upvotes: 1

Eric Fail
Eric Fail

Reputation: 7928

You can use NCOL() and NROW(), they treat vectors as 1-column matrix, i.e

x <- structure(c(1, 1, 1, 1, 1, 1, 1, 1, 1), .Dim = c(3L, 3L)) 
x
#>      [,1] [,2] [,3]
#> [1,]    1    1    1
#> [2,]    1    1    1
#> [3,]    1    1    1

Now, as you point out nrow(x[1,]) and nrow(x[2,]) return NULL

nrow(x[1,])
#> NULL
nrow(x[2,])
#> NULL

but, 

NCOL(x[1,])
#> [1] 1
NROW(x[1,])
#> [1] 3

You could also make the object a tibble, but I guess you don't want to go there with a matrix. Regardless,

# install.packages(c("tidyverse"), dependencies = TRUE)
library(tidyverse)

z <- x %>% as_tibble() 

nrow(z[1,])
#> [1] 1
ncol(z[1,])
#> [1] 3

Upvotes: 1

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