Creating a Histogram with Data from a File.dat in MATLAB

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  • Thread starter Thread starter quasarLie
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    Data Histogram Matlab
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Discussion Overview

The discussion revolves around creating a histogram in MATLAB using data imported from a file. Participants are addressing issues related to data filtering, histogram binning, and unexpected results in the histogram output.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant shares their initial MATLAB code for reading data and creating a histogram, seeking help to eliminate specific values (-9.9) from their dataset.
  • Another participant suggests assigning the filtered data back to R1 to remove unwanted values, or alternatively replacing them with NaN to preserve column indices.
  • A later reply indicates that the second suggestion results in unexpected values, specifically -9.9 and NaN, leading to confusion.
  • Participants discuss the importance of ensuring that the filtered data aligns with the bin edges used for the histogram, as misalignment could lead to incorrect histogram representation.
  • One participant expresses concern that their histogram does not reflect the expected distribution of data points, particularly around the value 0.4.
  • Another participant questions whether the data actually contains values within the specified bin range, prompting a review of the data points provided.
  • Discussion arises regarding potential floating-point errors in the bin edges created using the colon operator, which may affect how data points are binned.
  • Participants explore the implications of floating-point precision on binning, particularly for values that lie near the edges of bins.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of the proposed solutions for filtering data and the impact of floating-point errors on histogram accuracy. The discussion remains unresolved regarding the best approach to achieve the desired histogram output.

Contextual Notes

Limitations include potential floating-point errors affecting binning, the need for proper alignment of filtered data with histogram bins, and the uncertainty surrounding the actual data values present in the dataset.

quasarLie
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Hello everyone, I'm trying to make a MATLAB program which read a file.dat and then do a histogram
This what I did

Matlab: 
Data2=importdata('Ma.DAT');
R1=Data2.data(:,17)
R1(R1>-9.9)
L = 0:0.1:8;
histc(R1,L)
bar(L,histc(R1,L),'histc')
xlabel('R1')
ylabel('counts')
[FONT=PT Sans, san-serif]I want to eliminate all the number = -9.9 present in my clomn (R1), How can i do that? i tried this R1(R1>-9.9) but it doesn't work :p can anyone help me please?
Thanks
 
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quasarLie said:
I want to eliminate all the number = -9.9 present in my clomn (R1), How can i do that? i tried this R1(R1>-9.9) but it doesn't work :p can anyone help me please?
Thanks

Try

R1 = R1(R1>-9.9) % Assign the new, "fixed" data back to R1

or, if you want to preserve the column indices,

R1(R1>-9.9) = NaN % These shouldn't appear in the histogram
 
Tnanks, the first one works, but the second one gives only value = -9.9 and Nan
 
quasarLie said:
Tnanks, the first one works, but the second one gives only value = -9.9 and Nan

Sorry, I meant R1(R1==-9.9)=NaN.
 
Thanks, the code doesn't give me the right x value et y value, do you have any idea why?
 
If you eliminate the R1 values that don't fit your criteria, but not the corresponding L values, then they won't line up.

If you have a picture or a more detailed description, that might help us understand the output you're getting.
 
It give me this histogram, which is not correct because i have 240 objects and B1 have value between 0 and 3.8 (by 0.1 step). and it should not be empty at the value=0.4
upload_2018-4-11_14-26-42.png
 

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Are you sure your data have values in the interval [0.4, 0.5)?
 
Yes, these are my data
0.70 0.10 0 0.80 0.80 1 0.80 1.2 0.60 2.50 0 0.5 0.70 0.60 0.10 0.60 0.70 0.60 0.10 0.20 0.70 3.1 0.40 0.3
0.500000000000000
0.800000000000000
0.100000000000000
0.200000000000000
1.50000000000000
0.800000000000000
1.60000000000000
0.200000000000000
1
1
0.200000000000000
0.900000000000000
0.300000000000000
0
0.600000000000000
0.400000000000000
0.100000000000000
1.10000000000000
0.600000000000000
1
0.200000000000000
0.200000000000000
0.100000000000000
0.700000000000000
1.40000000000000
1.40000000000000
1.10000000000000
0.400000000000000
0.900000000000000
0.600000000000000
1.80000000000000
0.100000000000000
0.900000000000000
1.10000000000000
0.700000000000000
0.300000000000000
0.400000000000000
2.90000000000000
0.300000000000000
0.300000000000000
0.600000000000000
1.30000000000000
0.600000000000000
1.50000000000000
0.100000000000000
0.100000000000000
0.600000000000000
1.60000000000000
0.200000000000000
1.50000000000000
0.200000000000000
0.600000000000000
0.300000000000000
1.10000000000000
0.500000000000000
0
1
0.400000000000000
0.400000000000000
4
0.200000000000000
0.100000000000000
0.900000000000000
0.700000000000000
0.800000000000000
0.500000000000000
0.300000000000000
0.700000000000000
0.300000000000000
0.900000000000000
1
0.900000000000000
0.600000000000000
0.600000000000000
2.50000000000000
0.600000000000000
0.400000000000000
0.100000000000000
0.800000000000000
2.30000000000000
0.900000000000000
0.200000000000000
0
0.200000000000000
0.500000000000000
3
1.20000000000000
7.50000000000000
1.30000000000000
0.300000000000000
0
1
1.70000000000000
0.400000000000000
1.50000000000000
0.700000000000000
0.200000000000000
0.400000000000000
0.400000000000000
0.100000000000000
0.100000000000000
0.800000000000000
3.70000000000000
3.40000000000000
0.300000000000000
0.100000000000000
0.400000000000000
0
1.20000000000000
0
0.800000000000000
0.100000000000000
0.100000000000000
0.100000000000000
0.300000000000000
0.500000000000000
1.40000000000000
0.400000000000000
0.400000000000000
0.400000000000000
0.100000000000000
1.10000000000000
0.400000000000000
0.400000000000000
0
0.100000000000000
0.300000000000000
0.700000000000000
0.500000000000000
 
Last edited:
  • #10
The unexpected behavior comes from your use of the : operator to make your array of bin edges, in the statement:
Code: 
L = 0:0.1:8;

There is a small floating point error in the bin edges that causes data points such as 0.300000000000000, which lie (almost) exactly at the edge between two bins, to be inconsistently included into one (intended) bin as opposed to the next.

To illustrate what is happening, try the following code:
Code: 
a = L - 0.3;
a(4)
 
  • #11
Soory but i really don't see how i can fix it. I tried what you said but it changes nothing iot gives the same histogram
 
  • #12
olivermsun said:
Are you sure your data have values in the interval [0.4, 0.5)?
olivermsun said:
The unexpected behavior comes from your use of the : operator to make your array of bin edges, in the statement:
Code: 
L = 0:0.1:8;

There is a small floating point error in the bin edges that causes data points such as 0.300000000000000, which lie (almost) exactly at the edge between two bins, to be inconsistently included into one (intended) bin as opposed to the next.

To illustrate what is happening, try the following code:
Code: 
a = L - 0.3;
a(4)
what do you mean by between two bins, why this happens only with 0.3 and 0.7??
 
  • #13
You are using histc() to break up the data into bins, with the border between bins at 0.0, 0.1, 0.2, ..., right?
How does it decide where to put the data point 0.300000000000000?
 

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