list manipulation - How do I replace a missing value in a column with the value immediately above throughout a table?

I have a large table (7000 rows × 17 columns) of terse textual data. In many of the columns, empty entries have been replaced with "." as a marker. Working from the top of the columns downward, I want to replace each successive "." with the data value (non-".") from above until the next data value is found; at which time I want to replace the next sequence of "." with the new data value etc. E.g.

x     -->  x  
"."   -->  x  
y     -->  y  
"."   -->  y  
"."   -->  y  
z     -->  z  

"."   -->  z

I need to do this for all rows of data. Any help would be greatly appreciated. -k-

Answer

How about

f[_, y_] := y
f[x_, "."] := x

fill[data_] := Transpose[FoldList[f, First[#], Rest[#]] & /@ Transpose[data]]

Comments

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