fprintf varying number of decimal places in a column

I have a column with mostly zeros and a few numbers. On the zero values I need them to display as 0.0 and the number values I need to display the actual number of decimals such as 1.23456789. What formatting can I use?

[Paolo]

A possible solution is to use two separate fprintf formats.

 if(~x)
     fprintf('%.1f\n',x);
 else
     fprintf('%.8f\n',x);
 end

Does that help?

[Walter Roberson]

It is possible to vectorize but it uses an facility of fprintf that most people do not know.

[Paolo]

Can you share an example Walter?

[Anna Cole]

This is my trial code. What do I put in the place of the ~x in your code Paolo?

b=zeros(10,1);
b(5)=4.56987;
b(6)=6.4;
a=[1:1:10]';
d=[a,b];
fileID = fopen('fprintftrial.txt','w');
fprintf(fileID,'%.f,%.5f\n',[d]');
fclose(fileID);

[Walter Roberson]

The %.*f facility to pass in a width.

[Anna Cole]

I tried the %.*f earlier and this was the result

[dpb]

You used the '*' in the format string but didn't pass a corresponding vector of values to fill the place holder so fprintf used the next data from d when needed, leaving shorthanded as far as actual data to print.

Answer 1

[Walter Roberson]

b=zeros(10,1);
b(5)=4.56987;
b(6)=6.4;
a=[1:1:10]';
c = 5 * ones(length(a),1);
c(b==0) = 1;
d=[a,c,b];
fileID = fopen('fprintftrial.txt','w');
fprintf(fileID, '%d,%.*f\n', d');
fclose(fileID);

Result looks like

1,0.0
2,0.0
3,0.0
4,0.0
5,4.56987
6,6.40000
7,0.0
8,0.0
9,0.0
10,0.0