Writematrix loses precision with string present in data

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Martin
Martin 2025-3-18
回答： Walter Roberson 2025-3-18
I am saving a matrix to file and need full precision in the data. I am using the writematrix function, and my problem can be shown in this minimal example:
writematrix([1;0.123456789],"./testA.txt")
writematrix(["Test";0.123456789],"./testB.txt")
Then testA.txt:
1
0.123456789
And testB.txt
Test
0.12346
Is there a way to have strings (such as a header row) in my matrix but retain the full precision in the data?

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采纳的回答

Walter Roberson
Walter Roberson 2025-3-18
Ran in:
writematrix(["Test";compose("%.999g", 0.123456789)],"./testB.txt")
dbtype testB.txt
1 Test 2 0.12345678899999999733605449137030518613755702972412109375
Retains full precision.

更多回答（1 个）

dpb
dpb 2025-3-18
移动：dpb 2025-3-18
Ran in:
["Test";0.123456789]
ans = 2x1 string array
"Test" "0.12346"
The problem, if there is one, is in combining the string and the numeric into one array; MATLAB can have only one data type in an array other than a cell array and so the numeric value was coerced to a string before it was written; ergo, it isn't writematrix that is the issue here, it's trying put a square peg in a round hole; mixing data types inappropriately.
Probably the easiest workaround with the minimal example would to use a table instead...
tT=table(0.123456789,'VariableNames',"Test")
tT = table
Test _______ 0.12346
writetable(tT,"testB.txt",'WriteVariableNames',1)
type testB.txt
Test 0.123456789

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