How to get the first row of a dataframe with names when there is only one column?

When extracting a dataframe using [ by default drop argument is TRUE.

From ?Extract

drop - If TRUE the result is coerced to the lowest possible dimension.

Also you can check the class for both the dataframe after extracting the row.

df1 = data.frame(A=c(12,13), B=c(24,25))
df2 = data.frame(A=c(12,13))

class(df1[1, ])
#[1] "data.frame"
class(df2[1, ])
#[1] "numeric"

As we can see df2 is coerced to a vector. Using drop = FALSE will keep it as dataframe and not drop the dimensions.

df2[1,, drop = FALSE]
#   A
#1 12

class(df[1,, drop = FALSE])
#[1] "data.frame"

From dplyr

?slice

Choose rows by their ordinal position


library(dplyr)
slice(df, 1L)

#   A
#1 12

str(slice(df, 1L))
# 'data.frame': 1 obs. of  1 variable:
#$ A: num 12

If you want it to be a named number, you can unlist it.

str(unlist(slice(df, 1L)))
#Named num 12
# - attr(*, "names")= chr "A"

You can as well transpose it keeping column names.

colnames(t(unlist(slice(df, 1L))))

#"A"

If you want a named vector, then a single column data frame can be tricky to extract. A potential workaround can be,

do.call(c, df)[1]
#A1 
#12

Where,

str(do.call(c, df)[1])
 Named num 12
 - attr(*, "names")= chr "A1"

Note that since it converts all the values to named vector, it adds a numeric suffix after the name so it does not have duplicated names

Related