Creating new columns

Data Manipulation in Julia

Katerina Zahradova

Instructor

Columns vs. rows

Column

Single number for all rows
E.g., mean, median, sum, ...

Rows

Values depend on data in each individual row

=> using ByRow()

Flipper length to inches

# Convert mm to inches
transform(penguins, :flipper_length_mm => ByRow(x -> x/25.4) => :flipper_length_inch)

333x8 DataFrame
Row species   island    ...  body_mass_g  sex      flipper_lenght_inch
    String15  String15  ...  Int64        String7  Float64 
___________________________________________________________________
1   Adelie    Torgersen ...  3750         MALE     7.12598
2   Adelie    Torgersen ...  3800         FEMALE   7.32283
...

Culmen depth and length ratio

# Select columns and calculate their ratio
select(penguins,:culmen_depth_mm, :culmen_length_mm, 
   [:culmen_depth_mm, :culmen_length_mm] => ByRow((x, y) -> x/y) => :culmen_ratio)

333x3 DataFrame
Row  culmen_depth_mm  culmen_length_mm  culmen_ratio
     Float64          Float64           Float64
_____________________________________________________
1    18.7             39.1              0.478261
2    17.4             39.5              0.440506
...

New column from a vector

# Vector id_vec that we want to add


# Using [] and :
penguins[:, :id_colon] = id_vec


# Using [] and !
penguins[!, :id_exclamation] = id_vec


# Using .
penguins.id_dot = id_vec

Copy or not

penguins[:, :id_colon] = id_vec
penguins[!, :id_exclamation] = id_vec
penguins.id_dot = id_vec

# Change first element
id_vec[1] = 27
select(penguins, :species, r"id")

333x4 DataFrame
Row  species   id_colon  id_exclamation  id_dot
     String15  Int64     Int64           Int64
_____________________________________________________
1    Adelie    25        27              27
...

Copy or not

penguins[:, :id_colon] = id_vec        # copies values to the DataFrame
penguins[!, :id_exclamation] = id_vec  # references id_vec
penguins.id_dot = id_vec               # references id_vec

# Change first element
id_vec[1] = 27
select(penguins, :species, r"id")

333x4 DataFrame
Row  species   id_colon  id_exclamation  id_dot
     String15  Int64     Int64           Int64
_____________________________________________________
1    Adelie    25        27              27
...

Let's practice!

Data Manipulation in Julia