The sorted file is not saved correctly [closed]

Question

If I sort a file, I want save it in the new one. I use for this just:

sort -nk{fieldnumber} test.json > testsort.json

In the output the columns are shuffled and the column, which I have sorted, is in random order (not ascending). Why is it happen? Also, I want split this sorted file in many parts. I wish all parts are also sorted by the column, like here:

partaa
{'a':'a', 'b':'b', 'c':1}
{'a':'a', 'b':'b', 'c':1}
{'a':'a', 'b':'b', 'c':2}

partab
{'a':'a', 'b':'b', 'c':2}
{'a':'a', 'b':'b', 'c':3}
{'a':'a', 'b':'b', 'c':3}

partac
{'a':'a', 'b':'b', 'c':4}
{'a':'a', 'b':'b', 'c':5}
{'a':'a', 'b':'b', 'c':6}

I use for it

split -l 100 testsort.json part

Anyway, I have the all time the shuffled, unordered output. (for example some value from partac could be lesser then from partab)

PS

Thank you, I have found the problem someself. The input was corrupt, because some lines have additional fields.

{'a':'a', 'b':'b', 'c':2}
{'a':'a', 'b':'b', 'c':1}
{'a':'a', 'b':'b', 'c':2}
{'a':'a', 'b':'b', 'd':'d', 'c':1}
{'a':'a', 'b':'b', 'c':3}
{'a':'a', 'b':'b', 'f':'f', 'c':4}

I construct next regular expression, which search for certain field, take the numeric values, bring them in the front and sort them

sed -e 's/^\(.*columnname\)\([^,]*\)/\2\t\1\2/;s/^[" :]*//' test.json | sort -nk1 |sed -e 's/^[^{]*//' > testSort.json

Answer 1

The field separator of sort is not specified in your command:

sort -nk25

By default, the field separator of sort consists of whitespace¹.
That means you sort on the 25th field of 3 fields. It's not really clear on what you want to sort - but you could try to sort on whitespace separated column 3 with:

sort -nk3

Depending on what exactly you see as columns, you may run into the problem that the field separator can only be a single character, not a set of characters, (or even a regular expression) - except for the special case described below.
So you can use the quote as field separator, like sort -t"'" ..., and sort on the character values; It does not work like this with the numbers, because they are not quoted.

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(1): The default field separator does not consist off a single or fixed count of space characters. The separator is a non-blank to blank transition - that makes any string of whitespace that does not start in the first column a separator.