Returning line before after searching for pattern

I am reading a text file and want to return the line before after encountering search criteria.

The data looks like:

Test 1

X

1

1

1

1

Test 2

X

1

1

1

So I would like to search for X and return the line before.

I was able to return X but not the line before. Thanks!

readfile = readlines(filename); %filename is a .txt file
pat = " X "; %pattern
A = contains(readfile,pat);
display = readfile(A);

Answer 1

[Steven Lord]

A is a logical array with the same number of rows as the string array readfile. So if you remove/ignore the first element of A, it uses the logical value for row 2 to determine whether or not to select row 1, the logical value for row 3 to determine whether or not to select row 2, etc.

readfile = readlines("sampleText.txt")

readfile = 11×1 string array
    "Test 1"
    "X"
    "1"
    "1"
    "1"
    "1"
    "Test 2"
    "X"
    "1"
    "1"
    "1"

pat = "X";
A = contains(readfile,pat)

A = 11×1 logical array
   0
   1
   0
   0
   0
   0
   0
   1
   0
   0
   0

linesContainingX = readfile(A)

linesContainingX = 2×1 string array
    "X"
    "X"

linesBeforeX = readfile(A(2:end))

linesBeforeX = 2×1 string array
    "Test 1"
    "Test 2"

Note that if the first line of the file matches the pattern, starting your indexing using element 2 of A will skip that line in linesBeforeX; but then again, there isn't a "line before" the first line.

linesContainingTest = contains(readfile, "Test")

linesContainingTest = 11×1 logical array
   1
   0
   0
   0
   0
   0
   1
   0
   0
   0
   0

linesBeforeContainingTest = readfile(linesContainingTest(2:end))

linesBeforeContainingTest = "1"