# cluster\_infomap results not reproducible despite set.seed() **URL:** \ **Category:** Usage\ **Tags:** R\ **Created:** [24 July 2023 14:30 UTC](https://igraph.discourse.group/t/cluster-infomap-results-not-reproducible-despite-set-seed/1618 "2023-07-24T14:30:15Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![astruck](https://avatars.discourse-cdn.com/v4/letter/a/f6c823/32.png) [@astruck](https://igraph.discourse.group/u/astruck)\ **Post date:** [24 July 2023 14:30 UTC](https://igraph.discourse.group/t/cluster-infomap-results-not-reproducible-despite-set-seed/1618/1 "2023-07-24T14:30:15Z")
As Infomap incorporates a random walker, different results are expected. However, if I use `set.seed` from R – as suggested in this [post](https://igraph.discourse.group/t/warning-message-in-community-detection-with-cluster-edge-betweenness-algorithm/616/8) – the clusterings differ. The algorithm `cluster_leiden` does seem to recognize a set seed according the manual page 82. The old Infomap code offered a parameter `--seed`. [Link](https://www.mapequation.org/code_old.html#Options) I’d appreciate reproducible results from a clustering algorithm. I’m aware this is not trivial and the Infomap code is old. Is there anything you could do? Or should I use the modern implementation from [mapequation.org](https://www.mapequation.org/infomap/#ParamsAccuracy)? Thank you ---
**Author:** ![szhorvat](https://yyz2.discourse-cdn.com/free1/user_avatar/igraph.discourse.group/szhorvat/32/3_2.png) [@szhorvat](https://igraph.discourse.group/u/szhorvat)\ **Post date:** [24 July 2023 16:39 UTC](https://igraph.discourse.group/t/cluster-infomap-results-not-reproducible-despite-set-seed/1618/2 "2023-07-24T16:39:53Z")
I cannot reproduce this issue. If I set the same seed, I get the same clustering. Can you provide a reproducible example that demonstrates the problem? Run the example in a fresh R session and include the output of `sessionInfo()` in your report. ---
**Author:** ![szhorvat](https://yyz2.discourse-cdn.com/free1/user_avatar/igraph.discourse.group/szhorvat/32/3_2.png) [@szhorvat](https://igraph.discourse.group/u/szhorvat)\ **Post date:** [24 July 2023 16:47 UTC](https://igraph.discourse.group/t/cluster-infomap-results-not-reproducible-despite-set-seed/1618/3 "2023-07-24T16:47:29Z")
Example: ```r > library(igraph) Attaching package: ‘igraph’ The following objects are masked from ‘package:stats’: decompose, spectrum The following object is masked from ‘package:base’: union > set.seed(123) > g<-sample_gnm(100,200) ``` Without setting a seed, the results are different for each run: ```auto > cluster_infomap(g)$codelength [1] 6.0551 > cluster_infomap(g)$codelength [1] 6.054886 > cluster_infomap(g)$codelength [1] 6.063068 ``` With a seed, the results are deterministic: ```auto > set.seed(345); cluster_infomap(g)$codelength [1] 6.036988 > set.seed(345); cluster_infomap(g)$codelength [1] 6.036988 > set.seed(345); cluster_infomap(g)$codelength [1] 6.036988 ``` Session info: ```auto > sessionInfo() R version 4.3.1 (2023-06-16) Platform: x86_64-apple-darwin20 (64-bit) Running under: macOS Ventura 13.4.1 Matrix products: default BLAS: /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib LAPACK: /Library/Frameworks/R.framework/Versions/4.3-x86_64/Resources/lib/libRlapack.dylib; LAPACK version 3.11.0 locale: [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8 time zone: Europe/Berlin tzcode source: internal attached base packages: [1] stats graphics grDevices utils datasets [6] methods base other attached packages: [1] igraph_1.5.0 loaded via a namespace (and not attached): [1] compiler_4.3.1 magrittr_2.0.3 cli_3.6.1 [4] tools_4.3.1 rstudioapi_0.15.0 rlang_1.1.1 [7] pkgconfig_2.0.3 ``` ---
**Author:** ![astruck](https://avatars.discourse-cdn.com/v4/letter/a/f6c823/32.png) [@astruck](https://igraph.discourse.group/u/astruck)\ **Post date:** [25 July 2023 12:19 UTC](https://igraph.discourse.group/t/cluster-infomap-results-not-reproducible-despite-set-seed/1618/4 "2023-07-25T12:19:47Z")
It was helpful to see that you executed set.seed _every time_ before clustering. I understood the R function help as if it was sufficient to set it once. Thank you! ---
**Author:** ![szhorvat](https://yyz2.discourse-cdn.com/free1/user_avatar/igraph.discourse.group/szhorvat/32/3_2.png) [@szhorvat](https://igraph.discourse.group/u/szhorvat)\ **Post date:** [25 July 2023 16:35 UTC](https://igraph.discourse.group/t/cluster-infomap-results-not-reproducible-despite-set-seed/1618/5 "2023-07-25T16:35:55Z")
If you set the seed at the top of a script (sequence of commands), that script will execute identically every time. But that does not meet that multiple calls of a command within a script yield the same result. Example: ```auto > set.seed(123) > g<-sample_gnm(100,200) > cluster_infomap(g)$codelength [1] 6.0551 > cluster_infomap(g)$codelength [1] 6.054886 > cluster_infomap(g)$codelength [1] 6.063068 > set.seed(123) > g<-sample_gnm(100,200) > cluster_infomap(g)$codelength [1] 6.0551 > cluster_infomap(g)$codelength [1] 6.054886 > cluster_infomap(g)$codelength [1] 6.063068 ``` As you can see, the three runs after `set.seed` give different result. But after a repeated `set.seed` (with the same seed) the same three runs give the same three results again. ---
**Author:** ![astruck](https://avatars.discourse-cdn.com/v4/letter/a/f6c823/32.png) [@astruck](https://igraph.discourse.group/u/astruck)\ **Post date:** [26 July 2023 06:49 UTC](https://igraph.discourse.group/t/cluster-infomap-results-not-reproducible-despite-set-seed/1618/6 "2023-07-26T06:49:45Z")
What I did was set a seed, register a parallel compute backend and then used the `foreach` package to cluster the same data with what I assumed to be same seed on several cores. Now I know better. Thanks again. Apparently, the state of the RNG is changed after the function call (to my limited understanding) and the user-provided seed is only utilized once. Interestingly, the `codelength` was the same for all my clustering solutions but `modularity` value and community count differed.