How do you get up to first n characters in a string?

I have an array of strings of variable length s_arr. I want to limit the strings to only contain the first 3 elements. Some of the string have less than 3 elements, in which case they should be unchanged. I tried

arrayfun(@(s) s(1:3), s_arr)

but this gives an error when it finds a string with fewer than 3 elements. Why does MATLAB give an error and not just return the string unchanged? How can I achieve this goal?

Answer 1

[Image Analyst]

% Character array
charArray = 'abcdefgh'	% Single quotes
n = 3
out = charArray(1:n) % Another way
% String
str = "abcdefgh" % Double quotes
n = 3
charArray = char(str)
out = charArray(1:n)

charArray =

'abcdefgh'

n =

3

out =

'abc'

str =

"abcdefgh"

n =

3

charArray =

'abcdefgh'

out =

'abc'

[Image Analyst]

For the case where n is longer than the string, or less than the string (so more general and robust):

% Character array
charArray = 'ab'	% Single quotes
n = 30
out = charArray(1:min(length(charArray), n)) % Another way
% String
str = "ab" % Double quotes
charArray = char(str)
out = charArray(1:min(length(charArray), n))

Answer 2

[Star Strider]

I’m not certain what the arguments are, so I can’t test this with an array, however it works with individual argument.

Perhaps:

sfcn = @(s) s(1:min(numel(s),3));

then using ‘sfcn’ in the arrayfun call will produce the desired result.

.

[Image Analyst]

Works with a character array string, but not a string class string:

% Character array
charArray = 'abcdefgh'	% Single quotes
% String
s = "abcdefgh" % Double quotes
sfcn = @(s) s(1:min(numel(s),3))
out1 = sfcn(charArray)
out2 = sfcn(s)

charArray =

'abcdefgh'

s =

"abcdefgh"

sfcn =

function_handle with value:

@(s)s(1:min(numel(s),3))

out1 =

'abc'

out2 =

"abcdefgh"

[Star Strider]

I know it doesn’t work with string arrays, and neither does any sort of indexing because of the nature of string arrrays. However since some sort of indexing works, the arguments must be char (character) arrays. I am just not certain what the array of character arrays itself is. An array of string variables would have to be converted to char arrays for that sort of indexing to work, so I believe we can safely assume they are in fact char arrays.

sfcn = @(s) s(1:min(numel(s),3));
s_arr = {'abcde','fghi','jkl','mn','o'};

It will not work with cell arrays directly:

Out = arrayfun(sfcn, s_arr)

Out = 1×5 cell array
    {'abcde'}    {'fghi'}    {'jkl'}    {'mn'}    {'o'}

However it would work with cell array addressing:

Out = arrayfun(@(s)sfcn(s{:}), s_arr, 'Unif',0)

Out = 1×5 cell array
    {'abc'}    {'fgh'}    {'jkl'}    {'mn'}    {'o'}

or using cellfun instead of arrayfun:

Out = cellfun(sfcn, s_arr, 'Unif',0)

Out = 1×5 cell array
    {'abc'}    {'fgh'}    {'jkl'}    {'mn'}    {'o'}

So, we’re left to guess as to what the array is, since it isn’t presented.

Nevertheless, my function works with char arrays, and returns the desired result.

.

[Image Analyst]

Yeah, it would be nice if strings could use indexing like character arrays. I guess we need to use extractBefore() like @Paul showed, though you have to know about that function in advance, and it's not widely known like normal indexing it.

[Star Strider]

My guess is that they’re actually character arrays, so the indexing in the original post, and my adaptation of it to work with character arrays that are less than 3 characters in length, would work.

.

Answer 3

[Paul]

s_arr = ["a";"ab";"abc";"abcd";"abcde"]

s_arr = 5×1 string array
    "a"
    "ab"
    "abc"
    "abcd"
    "abcde"

s_arr(strlength(s_arr)>3) = extractBefore(s_arr(strlength(s_arr)>3),4)

s_arr = 5×1 string array
    "a"
    "ab"
    "abc"
    "abc"
    "abc"