If the condition on the file 2 value is not respected, the value of
file 1 is changed as NA.
The condition has 3 options : x< ("inf"), x>= ("sup"), < x <=
("between"). In case of error or by default, "inf" is considered.
In the cases "inf" and "sup", only one threshold is used (thrhd1) ;
in the case "between", two thresholds are needed (thrhd1 < thrhd2).
The output file is the name of the fist file with a cd_ prefix.