How to plot selectively from a colunm file

Hello rooters!

I am trying to selectively plot some data from a file with column, which isn’t .csv or .tsv
A typical file is

You can see that there is some info at first, which of course should be somehow skipped.
Then there are some column, from which I would like to plot one over the other. For instance the first column being x and the fourth being y.

How to do that?

I think it is also very confusing that latter, the 5 columns become 2 and it’s rather confusing how to pick the disired data.

Any ideas on that?

Thank’s a lot in advance!

Of course you need some code to open the file and read it line by line and parse each line to find the first line with “--------” line and the last line with “--------” in between them read the five columns and use the two desired ones. See for example the following two tutorial macros in ROOT how to do something like that: … ild.C.html … cle.C.html

Cheers, Fons.

Thank you very much for your answer!!!
I’ll check your links!!!

In the meantime I got help with a small code on C which does part of the job…

[code]#include <stdlib.h>
#include <stdio.h>

#define die(x) do {
fprintf(stderr, “Fatal: %s\n”, x);
} while (0)

#define MAX 10
#define MAXLEN 500

typedef struct { /* Text slice into a char buffer */
const char str; / start pointer /
int len; /
slice length */
} Slice;

int main(int argc, char *argv[])
int index[MAX]; /
column index /
int nindex = 0; /
number of columns to write /
Slice cols[MAX]; /
column substrings /
int context = 0; /
Are we scaning columns? */
int i;

if (argc < 3) die("Usage: col file columns ...");

for (i = 2; i < argc; i++) {
    int n = atoi(argv[i]);

    if (n < 1 || n > MAX) die("Illegal index");
    index[nindex++] = n - 1;

f = fopen(argv[1], "r");
if (f == NULL) die("Could not open file.");

for (;;) {
    char line[MAXLEN];

    if (fgets(line, MAXLEN, f) == NULL) break;

    if (context) {
        if (line[0] == '-') break;
        for (i = 0; i < nindex; i++) {
            int j = index[i];

            printf("    %.*s", cols[j].len, cols[j].str);

    if (line[0] == '-') {
        const char *p = line;
        int n = 0;

        while (*p == '-' || *p == ' ') {
            cols[n].str = p;
            while (*p == '-') p++;
            cols[n].len = p- cols[n].str;
            while (*p == ' ') p++;
            if (++n == MAX) break;

        for (i = 0; i < nindex; i++) {
            if (index[i] >= n) die("Columns index out of range");
        context = 1;

return 0;


It is run using

where data.txt is the “ascii” file and the numbers 2 4 6 indicate which columns are going to be processed.

The compile is done by using

The thing is that the output columns contain their units. Is there a way to get rid of the units and print the output in a seperate file?

Is there a chance that the execution of this code, could become in a macro along with the plot of the desired columns?