Join columns

Hi,

I have a sheet that is a calendar of activities, the rows are the dates and the columns the plots where the activities are carried out. The colums can be plots or subplots. My objective is to copy the activities of the plot into the colums of their correspondent subplots (keeping the activities that are only carried out in the subplot).

I have written a formula that works in a small test I did , but when I apply it to the calendar it does not work. I don't understand why.

Attached is the file. As example;
The column I is information of the plot
The column J is information of the subplot
I want to join them in the colum O. If you go, for example, to the cell O978, I get FALSE, instead of "hac_rk"


This is the formula:
=IF(ISBLANK(I978);J978;IF(OR(ISBLANK(J978);I978=J978);I978;FALSE))

The conditions are:
- If the plot is blank, nothing is done to the subplot
- If the plot is not blank and the subplot is blank or has the same information as the plot, we copy the information of the plot.
- If neither of them are blank and they are not the same, we get FALSE

The problem is that now I get FALSE when the subplot is blank and the plot is not.

Thanks a lot!