Arrays

[bumblebee]

Is there a preference in the CCSS for naming the size of arrays as “rows by columns” or “columns by rows?”

[Cathy Kessel]

If you search the CCSS document for the term “array,” you will find one example that involves different numbers of rows and columns: “The apples in the grocery window are in 3 rows and 6 columns. How many apples are in there?” (There are others in the Operations and Algebraic Thinking Progression.) The phrasing used is “3 rows and 6 columns” rather than “3 by 6.” That avoids the need to know whether “3 by 6” means “3 rows and 6 columns” or “6 rows and 3 columns.”

As discussed in the OA Progression (p. 24), seeing one array as a rotation of another (e.g., an array with 3 rows and 6 columns is a rotation of an array with 6 columns and 3 rows) can be used to illustrate the commutative property. So, at some point, students see that e.g., an array with 3 rows and 6 columns has the same number of objects as one with 6 rows and 3 columns.

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