Merge lists

Merge two lists of values without losing their original order. You can keep every occurrence or remove identical duplicates, then copy the list you get.

The tool reads the items of the first list, then those of the second. It trims spaces at the edges of each line and ignores empty lines. By default, duplicates are removed, including repeats inside the same list: only the first occurrence of each identical value is kept. The comparison is case-sensitive. Switch duplicate removal off if repetitions are meaningful. The result is not sorted. Before merging two sources, work out what each line represents: a name, a reference, an answer or a technical identifier. Removing duplicates helps when you want a directory of unique values, but it can lose information when a repeat stands for several real occurrences. If you combine two order logs, for instance, two identical lines may be two different orders; in that case, switch deduplication off. The order is predictable: items from the first list are processed before those from the second. When a duplicate is removed, the first occurrence is the one that stays, which preserves the priority of the first source. Duplicate matching is case-sensitive: “Client A” and “client a” are not strictly identical. Spaces at the ends of lines are trimmed, but variations inside values and typos are not corrected. The result is neither sorted nor checked against an external reference. For data reconciliation, first check formats and input conventions, then use a list comparison tool if you need to separate shared values from those found in only one source. Keep both original lists so you can rebuild the merge. A quick check is to count the useful lines of each input and compare the total with the result. With deduplication off, the number of output lines should equal the total of non-empty lines. With it on, the difference is the number of repeats removed.