# Calculating the value of an investors inventory

This is most likely a very trivial question but I thought I should ask since I have no one to talk to about it and also since a google search failed to turn anything up (I also searched this forum but couldn't find anything). I'm from a stats background doing some RA work and have no knowledge in finance, and I'm looking at some financial data at the moment and just wish to clarify something regarding investor profits. I have time series data from an investor who has shares in several companies and I also have the closing price of each of the shares for each day (The investor holds shares overnight which is why I have closing price data in particular).

For example, if we observe a single day of the year, the data is of a similar format to this:

`````` Stock  |   Inventory   |   Closing Price
--------------------------------------------------------
AAA     |    9          |   1.23
BBB     |    12         |   0.76
CCC     |   -34         |   4.58
DDD     |   -11         |   0.41
``````

(Note that inventory refers to the amount of the stock the investor holds overnight)

Now, I would like to calculate the value of the investors inventory at the end of each day (which is why I use closing prices). From the data I have, for stock AAA since I have an inventory of 9 and closing price of 1.23 then I think it is safe to assume that the investors' overnight value of AAA is merely 9*1.23 = \$11.07, and similarly for BBB it is 12*0.76 = \$9.12

However, I'm a little unsure what the correct way to calculate the investors' overnight value for CCC and DDD is. From what I have read, an investor can have negative inventory/stock through 'short-selling' and I assume that is what is happening in my situation. My question is, what is the correct way to calculate the value for these two stock? Is it just -34*4.58= -\$155.72 for CCC and -11*0.41= -\$4.51 for DDD? Or do I instead have to take the absolute value of the inventory such that I instead have 34*4.58 = \$155.72 and 11*0.41= \$4.51? Thanks in advance