[R] Dealing with missing data in ave() functions

[evelin.comper]

Dear all,

I would be grateful if you could help me in some way! Well, I have one
dataset already uploaded into R with some missing data. My dataset is made
of 19 columns, one of these is the sector (naf code). There are many rows
relating to the single enterprises. What I want to do is the mean of each
variable (column) by sector (naf code), so I type for example:

col_5 = data.frame(ave(x[,5], naf, na.rm = TRUE))

Col_5 is referred to the first variable of interest. But since there are
some missing data, it results in a series of NA all the column ahead (all
the rows are NA). How can I do to discard and not taking into account these
missing values??? How could I do to replace missing values with a simple
zero just for this analysis???

Thanks so much friends, bye!

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