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Epochs

Commands to define epochs for an EDF, and to attach annotations after loading an EDF

Command Description
EPOCH Specify epochs for an EDF
EPOCH-ANNOT Load epoch-wise annotations from a .eannot-format file

EPOCH

Divides the time series into equally-sized (possibly overlapping) epochs

Epoching an EDF is often a first a step that is required for many other Luna functions that work with epoched data. Although many commands that require epoched data will automatically set epochs (with a default 30-second duration), it is always good practice to set them explicitly in a script.

Parameters

Without parameters the default is 30-seconds, with no overlap (i.e. 30-second increments, equivalent to len=30 or epoch=30). In general, if the increment is not specified, it defaults to the epoch length (i.e. no overlap between epochs).

Parameter Example Description
len len=30 Epoch length (seconds), defaults to 30
inc inc=30 Epoch increment (seconds), defaults to len (i.e. no overlap)
epoch epoch=30,15 Epoch length{,increment} (seconds), defaults to 30,30
require require=10 Stop processing that EDF if there are not at least N epochs
verbose verbose Output epoch-level information

Outputs

Basic summary information (strata: none)

Variable Description
DUR Epoch duration (as per the input)
INC Epoch increment (as per the input)
NE Number of epochs in the EDF, given DUR and INC

Per-epoch interval information (option: verbose, strata: E)

Variable Description
E1 Current epoch number (which may differ from E if the EDF has been restructured)
HMS Clock-time for epoch start (hh:mm:ss)
INTERVAL String label of epoch interval (seconds)
MID Midpoint of epoch (seconds elapsed from EDF start)
START Start of epoch (seconds elapsed from EDF start)
STOP Stop of epoch (seconds elapsed from EDF start)

Example

To set epochs of 10-seconds, each with a 5-second overlap (output showing the first six epochs):

luna my.edf -o out.db -s "EPOCH len=10 inc=5 verbose" 

To get the number of epochs set:

destrat out.db +EPOCH
ID       DUR   INC   NE
nsrr01   10    5     8183
To get the exact location of each epoch:
destrat out.db +EPOCH -r E

ID      E   E1   HMS        INTERVAL       MID  START  STOP
nsrr01  1   1    21:58:17   0.00->10.00    5    0      10
nsrr01  2   2    21:58:22   5.00->15.00    10   5      15
nsrr01  3   3    21:58:27   10.00->20.00   15   10     20
nsrr01  4   4    21:58:32   15.00->25.00   20   15     25
nsrr01  5   5    21:58:37   20.00->30.00   25   20     30
nsrr01  6   6    21:58:42   25.00->35.00   30   25     35
... (etc) ...

If instead running this command, which first applies a MASK and RESTRUCTUREs the data, the

MASK epoch=10-14 & RE & EPOCH verbose
then the output would be as follows (i.e. note the difference between E and E1):
ID      E    E1   HMS        INTERVAL         MID   START  STOP
nsrr01  10   1    22:02:47   270.00->300.00   285   270    300
nsrr01  11   2    22:03:17   300.00->330.00   315   300    330
nsrr01  12   3    22:03:47   330.00->360.00   345   330    360
nsrr01  13   4    22:04:17   360.00->390.00   375   360    390
nsrr01  14   5    22:04:47   390.00->420.00   405   390    420

Info

The above command implicitly ran an EPOCH command prior to the MASK; as we only specified verbose for the second command, the output will be from the second EPOCH. In general, if you use the same command more than once in a script, it is a good idea to use TAGs to keep track of the output, as Luna will otherwise overwrite previous output from that command. For example:

MASK epoch=10-14 & RE & TAG R/2 & EPOCH verbose   
Output from the first (untagged) EPOCH:
destrat out.db +EPOCH 
ID      DUR    INC    NE
nsrr01  30     30     1364
Output from the second (tagged) EPOCH (tagged with R set to 2):
destrat out.db +EPOCH -r R
ID       R   DUR   INC    NE
nsrr01   2   30    30     5
i.e. note the difference in NE.

EPOCH-ANNOT

Attach epoch-level annotations from a file, to an epoched EDF

This command reads a plain-text file from disk, expecting the .eannot format. It is possible to apply multiple sets of annotations to epochs with multiple EPOCH-ANNOT commands.

The behavior of this command similar but not identical to what would happen if the .eannot file were directly specified in the sample-list (i.e. as any other XML, FTR or .annot annotation file). As this command can be performed after the EDF has been loaded and manipulated (e.g. via RESTRUCTURE), the number of epochs (i.e. rows in the file) should match exactly the number of epochs given the current state of the in-memory EDF (i.e. after any restructuring, and with the current epoch definitions).

That is, if EPOCH len=30 generates 1022 epochs for a given EDF, then the annotation file must be exactly 1022 epochs. Luna will give an error if the EPOCH command has not been performed prior to EPOCH-ANNOT.

In contrast, when attaching an .eannot file via the sample-list, Luna assumes the .eannot file corresponds to the entire on-disk EDF (typically with the default 30-second epochs).

Make sure to use plain-text files

As with all input to Luna, except the EDF itself, It is critical that the annotation file be a simple, plain-text file with no special encodings, not RTF (rich text format, etc). Please see this FAQ.

Parameters

Parameter Example Description
file file=annots/id1.epochs File path/name to read annotations from (required)
recode recode=NREM1=N1,NREM2=N2 Optional, comma-delimited list of recodings (from=to)

An optional recode parameter can be used to translate annotations on-the-fly.

Outputs

This command does not produce any output per se, other than noting the number of epoch/annotations read in the log/console, e.g.

 CMD #2: EPOCH-ANNOT
 mapping 2 distinct epoch-annotations (1022 in total) from annots/test.eannot

Example

Here we attach epoch-annotations to an epoched EDF and use them to mask out certain epochs. For example, here we have a dummy annotation file, that contains an annotation of either T or A for each epoch. This particular EDF has 1022 30-second epochs, and so the file epoch1.eannot is the same length:

$ sort epoch1.eannot | sort | uniq -c 
102 A 
920 T

The file epoch1.eannot is a simple text-file, with either an A or a T on each line, and nothing else.

Note

Annotations are not restricted to A or T or single characters: they can be any text string, but should not contain spaces or special characters. A common use may be if sleep staging has been performed, so each row indicates N1, N2, N3, REM or Wake, etc.

To attach this file, and use it to select only A epochs:

luna my.edf -s "EPOCH & EPOCH-ANNOT file=epoch1.eannot & MASK ifnot=A & RE"
 ..................................................................
 CMD #1: EPOCH
 set epochs, length 30 (step 30), 1022 epochs
 ..................................................................
 CMD #2: EPOCH-ANNOT
 mapping 2 distinct epoch-annotations (1022 in total) from epoch1.eannot
 ..................................................................
 CMD #3: MASK
 set masking mode to 'mask' (default)
 based on A 102 epochs match;  920 newly masked, 0 unmasked, 102 unchanged
 total of 102 of 1022 retained
 ..................................................................
 CMD #4: RESTRUCTURE
 restructuring as an EDF+ : keeping 3060 records of 30664, resetting mask
 retaining 102 epochs

That is, we've used an external annotation to select a set of epochs from an EDF. In real applications, one would subsequently apply other analysis commands, or write out a new EDF (see WRITE), for example.

Working with multiple EDFs

When using sample-lists to work with multiple EDFs, it is often convenient to use the ^ special character in a script, which is replaced with the ID (from the first column of the sample-list, not the EDF header) for that individual, which enables the same script to point to different annotations files for different individuals (assuming of course, that those annotation files are named to include that ID).

Here is an example of using a script (instead of the -s option) for achieve the same result as above, but here using a sample list and renaming the annotation file to, for example, annots/id001.epoch.eannot. We might specify the sample list s.lst as follows, to assign the ID id001 to the EDF:

id001    my.edf 

We would then write a Luna script file, say called extract.txt, which also illustrates using a variable (to specify more flexibly which annotation we want to select, e.g. A, or T or something else, if another annotation file were used) and writing a new EDF (with the WRITE command):

% Epoch the data (default 30 sec)

EPOCH

% Attach the matching file in the annots/ folder for this individual
% i.e. requires that files are named 

EPOCH-ANNOT file=annots/^.eannot

% Set this mask, where the value of ${x} will be specified 
% on the command line

MASK ifnot=${x}

% Apply the mask, actually restructuring the internal EDF
% (Note, RESTRUCTURE can be abbreviated as RE)

RESTRUCTURE

% Write a new EDF back to disk

WRITE edf-dir=edfs/            % write new EDFs in this directory/folder
      edf-tag=extract-${x}     % add this tag to the filename for each EDF
      sample-list=s-${x}.lst   % make a new sample-list to point to the new EDFs

Note how the ^ character is used to specify the individual/EDF ID. We can then run Luna, setting the x variable to A:

luna s.lst x=A < extract.txt 

When run for id001, for example, Luna looks for annots/id001.eannot, and attaches it. It then masks epochs that do not match the value specified by the variable ${x}, which in this case is set to A. After RESTRUCTURE-ing the internal EDF to remove the masked epochs, we WRITE it back out to a file, edfs/my-extract-A.edf and create a new sample list s-A.lst that points to this. As a sanity check, we can run a DESC command on the new project/sample-list:

luna s-A.lst -s DESC
which correctly shows a new EDF of 51 minutes (i.e. 102 30-second epochs).
EDF file          : edfs/my-extract-A.edf
ID                : id001
Duration          : 00:51:00
Number of signals : 6
Signals           : EOG-L[256] EOG-R[256] EMG[256] EEG1[256] EEG2[256] EEG3[256]

Naturally, the advantage of this approach is that it will work if a project (i.e. the s.lst) contains multiple EDFs:

id001   subj-1.edf
id002   subj-2.edf
id003   subj-3.edf
... (etc) ...
and the annots/ folder contains the corresponding annotation files for each subject:
annots/id001.eannot
annots/id002.eannot
annots/id003.eannot

That is, all EDFs can still be processed (and multiple new EDFs generated) with a single Luna command and without altering or copying the extract.txt Luna script.