how to dissolve line segments into long line?

Could it be that there are tiny imprecisions in the start/end vertices of the line segments? Perhaps try inserting a Snapper with end point snapping just before the LineCombiner. If that doesn't work, check if the LineCombiner works without the Group By-attributes -- if that's the case, then something is wrong with the Group By-attributes.

I used ESRI ArcMap tool box, a tool called dissolve, that can do the work without any issue. I don't specify snapping. just dissolve line segments base on same attribute values. it can be multiline while they are not adjacent. I am wondering if there is any transformer dedicated for dissolving line segments as same as ESRI's one?

Aggregator might suffice. It will create aggregates (groups) of lines

The ArcGIS toolboxes actually apply a tiny amount of "snapping" to all the features, according to the tolerance settings of the feature class. FME does not, which is why it may sometimes be necessary to use a Snapper with a very small tolerance to make sure all the vertices line up perfectly.

thanks for the help. Aggregator is not for this dissolving purpose I guess. it doesn't ask attribute based on.

I have to use ArcGIS toolboxes. I thought FME has everything ArcGIS toolboxes provided.😏

I am new for FME actually. I have FME case C657637 generated. but is any support to open the case?

Thats where you'd use group by. Populating the Group By field will only aggregate features that share a common value in the specified attribute(s)

https://docs.safe.com/fme/html/FME_Desktop_Documentation/FME_Transformers/Group_Based_Transformers.htm

The thing to note about comparing FME and ArcGIS is that on the surface, it looks like it is a one to one relationship (i.e one tool in FME does what one tool in AG does) but it isn't. Another thing to note is that FME operations on a feature by feature level (row by row) where as AG generally operates on a feature class by feature class (table by by table) basis. Two very different ways of processing data

Can you provide some sample data?

Generally what @david_r​ said about snapping should work. Maybe there is something you are missing.

You can check the progress of your support cases here: https://community.safe.com/s/case/Case/Default

Apples and oranges, as @hkingsbury​ is also alluding to. FME and ArcGIS are complementary, not 100% overlapping (what would be the use of that).

agree, "complementary" is good explanation.

The ‘use of that’ would be to use FME to automate processes that require both geoprocessing tools and data interoperability among the ever-growing number of software packages that we have to interact with.