Say we have a series of month-on-month figures like the following, and we want to get the growth rate between the two periods:
product aug sep growth apples 100 130 +30% oranges 30 90 +200% pears 70 140 +100% bananas 210 220 +5%
Easy enough, but how about if there is one product which didn't sell in August:
berries 0 10 ??
If we want to display berries in the same table as the other ones, we have a problem. The naive way would be to display something like "NaN" or "N/A" but this would have the drawback of not being very informative as to "how much" berries have gone up, compared to the other products. For instance, had we sold 1600 berries in September, or had we sold only one, this "N/A" value would appear exactly the same. In one case though, berries have seen an extreme surge, and in the other, just one has been sold, almost inconsequentially.
Another way would be to add "1" to the previous-month figure, which would solve the "N/A" problem but would make all the other figures slightly off, in addition to making the concerned value extremely high (e.g. if 0 berries in Aug and 10 berries in Sep, then the growth rate would be (10 - 1) / 1 = 900% which would dwarf any other product even though 10 is not that high of a value, compared to the rest of the table).
How to make such notion of a growth, even when coming from zero, appear in the final table, while keeping the table consistent and the values with non-zero origin correct?