Parsing table of string without looping

Hello,

I have a table of string (name : polystring 300 000 x 1 table) where each string register a set of gps coordinates that defines a polygon.

For instance, one string can be : 2.331878 48.866003, 2.331872 48.866107, 2.331855 48.866211, 2.331825 48.866314, 2.331785 48.866416, 2.331733 48.866517, 2.331669 48.866617, 2.331595 48.866715, 2.331509 48.866811

Each got a different number of points (from a few to 200 points or so).

By using this command :

B = cellfun(@(x) strsplit(x, ", ")', polystring, 'uni', false);

I managed to create an array of cells (300 000 x 1 cell) where each cell is a (N x 1 cell). Each cell is storing a string like "2.331878 48.866003"

I would like now to parse the cells to have a (300 000 x 1) with each cell being a (N x 2) matrix, by parsing my previous (N x 1) using " " as a splitter.

I do not get how I should do it as using

C = cellfun(@(x) str2double(strsplit(x, " ")), B, 'uni', false);

Trigger an error 'First input must be either a character vector or a string scalar.'

Ultimately, the aim is to create polygon (polyshape(P) with P being my Nx2 matrix of GPS coordinates)

A warm thanks for any help or hint provided

[Guillaume]

Note that if the initial table of strings is the result of a text file import a much more efficient solution would be to fix the import so that it imports the data directly as a numeric array/table. To help with that, we need the details of the text file.

Answer 1

[Stephen23]

Rather than slow and complex string manipulation you can easily use sscanf to directly convert each string into a numeric matrix:

>> str = '2.331878 48.866003, 2.331872 48.866107, 2.331855 48.866211, 2.331825 48.866314, 2.331785 48.866416, 2.331733 48.866517, 2.331669 48.866617, 2.331595 48.866715, 2.331509 48.866811';
>> sscanf(str,'%f%f,',[2,Inf]).'
ans =
    2.3319   48.8660
    2.3319   48.8661
    2.3319   48.8662
    2.3318   48.8663
    2.3318   48.8664
    2.3317   48.8665
    2.3317   48.8666
    2.3316   48.8667
    2.3315   48.8668

Repeat for each cell.

[PsykotropyK]

Great thanks, using it with cellfun made the trick :

B = cellfun(@(x) sscanf(x,'%f%f,',[2,Inf]), polystring, 'uni', false);

And ultimately to create the polygons

B = cellfun(@(x) polyshape(sscanf(x,'%f%f,',[2,Inf])'), polystring, 'uni', false);

[Stephen23]

@PsykotropyK: I hope that it helps. Note that it is a good habit to use a normal element-wise transpose .' unless you specifically need the complex conjugate transpose '