Characters and Strings

1Character vectors

Text in single quotes is a character vector, class char: a row of characters, one per letter. 'sub-01' is 1 row by 6 characters, and you can index single characters just like numbers in an array.

subj = 'sub-01'
class(subj)
size(subj)
subj(1:3)
subj(end)

2Strings

Text in double quotes is a string, class string. A string holds the whole piece of text as one value, so its size is 1-by-1. strlength counts its characters.

s = "sub-01"
class(s)
size(s)
strlength(s)

Strings arrived in newer versions of MATLAB. EEGLAB is written around character vectors, so use single quotes for file names and options you pass to EEGLAB.

3Joining text

Character vectors join with square brackets, the same way arrays do. Strings join with +.

['sub-' '02' '.set']
"sub-" + "02" + ".set"

4Numbers inside text

To put a number into a file name, turn it into text first. num2str does that. sprintf fills a template: %d is a whole number, %02d pads it to two digits, %s is text, and %.1f is a number with one decimal.

n = 3;
['sub-0' num2str(n) '.set']
sprintf('sub-%02d.set', n)
sprintf('sub-%02d.set', 12)
sprintf('%s filtered at %.1f Hz', 'sub-03', 0.1)

With %02d, participant 3 becomes sub-03 and participant 12 becomes sub-12, so one template covers everyone. Lesson 8 uses this in a loop.

5Two traps

Adding a number to a character vector does not join them. MATLAB turns each character into its character code and adds to that. And == compares text one character at a time, so it fails when the lengths differ. Use strcmp to ask whether two pieces of text are the same.

'sub-' + 1  # four numbers, not 'sub-1'
strcmp(subj, 'sub-01')
subj == 'sub-1'