data.label wrong after componentanalysis?

[Nathan Weisz]

hi everyone,

for an analysis of EEG data i'm doing some ICA cleaning. since there
are many conditions / epochs, i do the ICA on a subset of trials and
then apply the calculated mixing matrix to the individual conditions.

i noticed (and i'm quite sure it's no user related error) that after
rejecting components and reconstructing the preprocessing data
structure, that the sequence in data.label has changed (apparently
into alphabetical order). however that rows in the 2-D matrices making
up data.trial(xy) have not changed, accordingly. i noticed because the
topography of the auditory N1 was a huge mess.

changing the labels solved the problem, i.e.:
ica_cleaned_data.label = data_before_ica_cleaning.label;

for those interested here the original code:

load([outdir '/dataB1F1.mat'], 'dataB1F1') %load data for one condition

cfg=[];
cfg.topo=comp.topo;
cfg.topolabel=comp.topolabel;

tmpcomp=componentanalysis(cfg,dataB1F1); %apply precomputed ICA to
condition

cfg=[];
cfg.component=ncmp;

dataB1F1=rejectcomponent(cfg, tmpcomp); %reject components obviously
representing artefacts

 >> [comp.cfg.channel(1:5) tmpcomp.cfg.channel(1:5)] %demonstrate
channel label mismatch

ans =

     'Lm'     'L1'
     'LE1'    'L10'
     'LE2'    'L11'
     'LE3'    'L12'
     'LD2'    'L13'

the crucial line appears to be in componentanalysis line 220:
cfg.channel = intersect(cfg.channel, cfg.topolabel);

intersect sorts the outcome:
 >> a=randperm(10)

a =

      7     1     9     3     6     2     5     4    10     8

 >> b=randperm(10)

b =

      6     3     5     1     8     2    10     4     9     7

 >> intersect(a,b)

ans =

      1     2     3     4     5     6     7     8     9    10

since i use all channels, simply replacing the label-field with the
original label-field works for me.

best,
nathan

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