/**
 * Remove duplicate column names in an array.
 */ export function uniqueColumnNames < T > ( columns ) { const a = columns . concat ( ) ; for ( let i = 0 ; i < a . length ; ++ i ) { for ( let j = i + 1 ; j < a . length ; ++ j ) { const left = a [ i ] ; const right = a [ j ] ; if ( left === right ) { a . splice ( j -- , 1 ) ; } else if ( ( Array . isArray ( left ) && Array . isArray ( right ) ) && left [ 1 ] === right [ 1 ] ) { a . splice ( j -- , 1 ) ; } } } return a ; }