I have a column in numbers like below
-0.01343
0.002
-1.1234
I want to align the column in vi editor like below
-0.01343
0.002
-1.1234
So, you want to insert a space before each line not starting with a minus:
The appropriate command is is :%s/^\([^-]\)/ \1/
This breaks down as:
: - start command
%s - regex on all lines
/^\([^-]\) - matching the start of the line, followed by any character other than -, which we will call group 1
/ \1 - replace with a space followed by whatever was in group 1
/ - end regex, perform no more than once on each line
Other options:
If you select the intended lines in a visual block, typing : will start the command with '<,'>. Then move onto the regex starting with s (no %) and it will apply only to the selected lines.
If you end it with a /c it will ask for confirmation on each replacement. If you end it with /g it will work multiple times per line if applicable. /gc is valid.
If you'd wanted the decimal points to be aligned, rather than the first digits, that's more complex and probably cannot be done with a simple command in vi or vim.