📂Julia

How to View the First and Last Parts of a DataFrame in Julia

Overview

In Julia, DataFrames do not have head or tail functions. Although it’s a bit annoying because it requires an extra step compared to other languages, you can use the first and last functions. Why does DataFrames.jl stubbornly ignore industry conventions? This can roughly be summarized as follows¹: :

1. There’s already a Base.tail function in Base, and they want to avoid conflicts.
2. first and last were already implemented for the same purpose before head and tail.
3. It’s preferable to keep function names as concise as possible, and head or tail are too common and short.

Code

using DataFrames

df = DataFrame(reshape(1:100, :, 5), :auto)

first

julia> first(df, 3)
3×5 DataFrame
 Row │ x1     x2     x3     x4     x5    
     │ Int64  Int64  Int64  Int64  Int64
─────┼───────────────────────────────────
   1 │     1     21     41     61     81
   2 │     2     22     42     62     82
   3 │     3     23     43     63     83

last

julia> last(df, 10)
10×5 DataFrame
 Row │ x1     x2     x3     x4     x5    
     │ Int64  Int64  Int64  Int64  Int64
─────┼───────────────────────────────────
   1 │    11     31     51     71     91
   2 │    12     32     52     72     92
   3 │    13     33     53     73     93
   4 │    14     34     54     74     94
   5 │    15     35     55     75     95
   6 │    16     36     56     76     96
   7 │    17     37     57     77     97
   8 │    18     38     58     78     98
   9 │    19     39     59     79     99
  10 │    20     40     60     80    100

If the second argument is omitted, it defaults to showing just one row.

julia> last(df)
DataFrameRow
 Row │ x1     x2     x3     x4     x5    
     │ Int64  Int64  Int64  Int64  Int64
─────┼───────────────────────────────────
  20 │    20     40     60     80    100

Environment

• OS: Windows
• Julia: v1.11.1
• DataFrames v1.7.0