flat(): how many levels to remove

Useful to know

flat() collects elements from nested arrays to a selected depth. By default it is one level : [1, [2, [3]]].flat() gives [1, 2, [3]]. With flat(2), the result is [1, 2, 3]. [1]

Select the depth according to the data structure. Indiscriminate removal of all levels can delete useful grouping, for example rows and columns. The new external array does not mean deep copying of every object inside; the method decides the list structure, not the independence of all data.