DataFrame.apply

Apply a function to each element or along a specified axis of a DataFrame.

danfo.DataFrame.apply(callable, options)

Parameters	Type	Description	Default
callable	Function	Function to apply to each column or row
options	Object	axis: 0 or 1. If 0, compute the power column-wise, if 1, row-wise	{axis: 1}

Examples

Apply a function along default axis 1 (columns)

Note that the specified function passed to apply will be called with an array of the values across the specified axis.

Node

const dfd = require("danfojs-node")

let data = [[1, 2, 3], [4, 5, 6], [20, 30, 40], [39, 89, 78]]
let cols = ["A", "B", "C"]
let df = new dfd.DataFrame(data, { columns: cols })

function sum_vals(col) {
    return col.reduce((a, b) => a + b, 0);
}

let df_new = df.apply(sum_vals, { axis: 1 })
df_new.print()

Browser

Output

╔═══╤═════╗
║ 0 │ 6   ║
╟───┼─────╢
║ 1 │ 15  ║
╟───┼─────╢
║ 2 │ 90  ║
╟───┼─────╢
║ 3 │ 206 ║
╚═══╧═════╝

Apply a function along axis 0 (row)

Node

const dfd = require("danfojs-node")

let data = [[1, 2, 3], [4, 5, 6], [20, 30, 40], [39, 89, 78]]
let cols = ["A", "B", "C"]
let df = new dfd.DataFrame(data, { columns: cols })

function sum_vals(col) {
    return col.reduce((a, b) => a + b, 0);
}

let df_new = df.apply(sum_vals, { axis: 0 })
df_new.print()

Browser

Output

╔═══╤═════╗
║ A │ 64  ║
╟───┼─────╢
║ B │ 126 ║
╟───┼─────╢
║ C │ 127 ║
╚═══╧═════╝