CODEWITHSUNDEEP
matrix
Icebone1000
Icebone1000

Reputation: 1321

How to get row and column from index?

I'm drawing a HUGE blank here.

Everything I've found is about getting an index from a given row and column, but how do I get a row and a column from an index?

The row is easy: (int)(index / width).

My brain is suffering massive bleed trying to compute the column.

Shame on me.

Upvotes: 41

Views: 40279

Answers (4)

paxdiablo
paxdiablo

Reputation: 881633

For a zero-based index, the two operations are, where width is the width of the structure:

row    = index / width
column = index % width

Those are for C using integers, where the division rounds down and the % modulo operator gives the remainder. If you're not using C, you may have to translate to the equivalent operations.

If you don't have a modulo operator, you can use:

row    = index / width
column = index - (row * width)

Upvotes: 83

AdamOutler
AdamOutler

Reputation: 900

In java, with a column offset of 1, this is a way to do it

int offset=1;
column = Math.floorDiv(location-offset , 3)+offset;
row = ( (location-offset) %3 )+offset ;

Upvotes: 0

StackUnderflow
StackUnderflow

Reputation: 2463

Swift 4

typealias ColumnRowType = (column:Int, row:Int)

func indexToColumnRow(index:Int, columns:Int) -> ColumnRowType
{
    let columnIndex = (index % columns)
    let rowIndex = /*floor*/(index / columns)    // we just cast to an `Int`

    return ColumnRowType(columnIndex, rowIndex)
}

Upvotes: 2

Nicolas Bodin
Nicolas Bodin

Reputation: 1591

Paxdiablo's answer is the right one. If someone needs the reverse process to get index from row and column: 

index = (row * width) + column

Upvotes: 27

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