# How to visualize NaNs in an array?
**URL:** https://discourse.julialang.org/t/how-to-visualize-nans-in-an-array/133738
**Category:** General Usage
**Tags:** question
**Created:** [November 7, 2025, 4:49pm UTC](https://discourse.julialang.org/t/how-to-visualize-nans-in-an-array/133738 "2025-11-07T16:49:32Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [November 7, 2025, 4:49pm UTC](https://discourse.julialang.org/t/how-to-visualize-nans-in-an-array/133738/1 "2025-11-07T16:49:32Z")
I have a 2D array of size 150x150, and for debugging purposes, I want to see in the REPL where the NaNs are in this array.
How would you do that?
---
### Author:  [@mbauman](https://discourse.julialang.org/u/mbauman)
#### Post date: [November 7, 2025, 4:54pm UTC](https://discourse.julialang.org/t/how-to-visualize-nans-in-an-array/133738/2 "2025-11-07T16:54:35Z")
Are the NaNs sparse? Use a sparse array! It’s quick and dirty, but… it’s quick 🙂
```julia-auto
julia> A = rand(150,150);
julia> A[A .< .1] .= NaN;
julia> using SparseArrays
julia> sparse(isnan.(A))
150×150 SparseMatrixCSC{Bool, Int64} with 2250 stored entries:
⎡⢐⠔⠂⡄⢆⡊⠢⢀⡀⠀⢠⢀⡄⢂⠁⡃⡀⢀⠔⢂⡀⢀⠂⢀⠀⠀⠀⡠⢐⠠⠐⡈⠆⠀⠋⠀⢨⢀⠉⢸⠁⡀⠓⠈⡃⠀⠠⢰⢒⢀⢈⠄⎤
⎢⠀⠈⠀⠱⠂⡠⠀⢀⠰⠀⠬⠈⠁⠣⢐⠈⠀⠰⠀⢠⢠⠀⠠⠈⠐⠄⠤⠐⠥⠜⠢⠀⠄⠂⡅⠠⠀⠀⠀⠀⠀⠄⠅⠆⠅⠂⠐⠠⠡⠄⠤⠀⎥
⎢⢩⠡⠀⠠⠁⠁⠀⡈⠁⠈⠈⠔⠈⠁⠡⠃⡘⠈⠐⠀⠡⠉⠄⠄⢄⠁⠐⠸⢉⠢⠀⠈⠌⠀⠩⢀⠠⠄⢠⢙⠁⡀⠉⢠⠅⠒⡀⢳⡀⠠⡢⠠⎥
⎢⢐⠠⠈⠒⠌⠄⡄⣀⠥⠀⠼⢀⠀⢐⡁⡁⠄⢐⠈⠁⠖⡊⡁⠁⠀⠀⠃⠂⠠⠄⠄⠡⠊⣈⢀⠤⢜⠀⡁⠝⠨⣅⣡⠀⡀⢀⣈⠀⣁⢀⢌⠀⎥
⎢⠒⠂⠂⠄⣅⡁⢀⢂⡀⣐⣃⠐⠀⠂⡆⢕⠀⠀⠀⣐⡐⠀⡆⡀⠕⡂⡐⡐⡐⢀⠆⠂⠛⣄⠐⠀⠐⢠⠀⡂⠇⠊⠃⠖⡂⢀⠀⠈⢀⣠⠂⣀⎥
⎢⢠⠰⣈⠘⠕⠁⠃⠐⡴⣐⠐⠀⠈⠂⠀⠃⡂⣂⠐⠸⠔⢀⠒⠑⠒⡅⠲⠀⠒⠀⠀⠞⠄⡆⠀⢀⢖⡰⡀⠐⢂⢀⠀⠲⠢⠂⠰⠸⠠⠀⡂⠂⎥
⎢⠡⠀⢊⠁⠀⣠⠈⠨⠀⠠⠀⡌⠬⠔⣁⡅⠠⢄⢁⠭⠠⠁⢀⠇⠂⠈⠈⠊⠀⢊⢈⠆⣄⠌⠄⠈⠃⢌⠀⠰⢀⠠⠡⡈⡀⠡⠐⠀⠠⡀⢄⠄⎥
⎢⠢⠨⠄⡤⠈⠇⡠⠀⢄⠉⠐⠁⠅⠠⠡⠀⠜⠤⠈⠠⢡⣠⠥⠁⠈⢄⠁⠀⡀⡄⠀⠥⡈⠙⠅⢉⠈⠈⠊⠀⠁⡀⠄⠁⠁⠂⡠⠈⠀⠀⢃⠅⎥
⎢⣈⠰⣄⣁⡇⠀⢉⠀⠔⢁⠀⠀⠈⢌⢀⠀⠀⠜⠂⡈⢃⠨⠄⡂⠁⠀⠈⠈⠌⢑⠀⠀⢀⠈⡂⡌⠰⠀⠈⠤⠈⡁⠁⣀⢉⠑⢀⡄⠀⢀⢊⠂⎥
⎢⢐⢀⠑⢒⠀⠀⠂⢀⣀⠂⠂⠁⠐⡆⠅⡂⠀⢀⠂⠀⢎⢀⡄⠂⡂⢀⣁⢁⢐⢒⡘⠄⠦⠄⠀⠀⠐⢲⠞⢢⢀⠀⠀⡂⡀⡀⠠⠀⠰⣂⣈⠈⎥
⎢⠖⠀⠀⠂⠠⠁⠂⠈⠀⢀⠁⢀⢀⠀⡪⠀⡀⠀⠀⠀⠀⡁⠀⢠⡠⢀⠀⠁⡫⠘⡔⠀⠂⢌⢄⠒⠀⠒⡠⠠⠐⡀⣂⡊⢂⠜⠀⢒⠀⠂⠂⠀⎥
⎢⡅⠠⠤⡉⠪⠠⠨⠸⠈⠭⠄⠈⠉⠀⡋⡥⡁⠅⠀⠄⠀⠃⡄⠀⠁⠄⠠⠠⠮⠐⡠⠁⠃⠄⢥⠊⢠⢨⢀⠹⠂⠈⡁⠑⢠⠱⠀⠄⢀⠈⠀⠠⎥
⎢⠄⠨⢤⠀⠨⠔⠀⠠⢼⡀⠀⠘⢄⡢⠀⢄⠀⠀⡌⠊⢀⠤⠌⠃⠐⠂⢍⠄⠀⠁⠀⠦⠀⡊⡃⠡⠐⠊⠠⠈⠀⠀⠌⠄⠁⢀⠀⠀⠨⠁⠅⠔⎥
⎢⠠⠰⠀⡥⢌⡀⡆⢈⠂⠈⠀⠀⠪⠂⡀⡀⢄⠢⠒⠐⠀⠀⡀⢀⢀⡂⠀⢄⡘⢑⢂⡂⠈⠀⠒⠀⠀⠔⠒⢓⠁⠀⠊⡀⡄⠀⠄⣀⢂⡄⠔⡢⎥
⎢⢔⢐⠀⢊⡀⣄⣗⢈⠠⣈⠺⢀⠀⠆⠀⡄⠀⠀⠐⠀⠀⠀⡴⢖⡟⠂⠀⡖⢂⠐⠠⡀⠀⠀⡄⠲⠠⢐⣐⠀⠀⡁⢂⠐⠀⢀⢌⠀⠀⠁⠀⠨⎥
⎢⠄⡀⠀⠅⠀⠠⠁⠐⠠⠁⠠⠀⡢⠄⡀⢈⠄⠀⠐⠀⢘⠂⠆⠤⠁⠄⠠⡂⠀⠠⠁⠀⠄⠄⠥⢰⣰⢄⢐⠄⠄⡄⡀⡀⠠⢡⠠⠈⡧⠨⠀⠀⎥
⎢⠁⣈⢃⢀⠥⠁⠁⠰⠖⠜⠁⠈⠄⠖⠄⠠⠂⢑⠨⡐⠀⠄⠍⢦⠄⠢⠍⠠⠡⠐⠀⠔⡄⠁⡀⠙⠨⠍⠰⠨⡀⠡⡇⠃⠀⠐⠈⠠⡇⠂⠋⠢⎥
⎢⢈⢉⢆⡀⣄⠀⡀⠘⠀⢀⢤⠀⣀⢅⡄⢈⠏⣁⢈⣡⢈⡁⡀⠁⠠⣄⢉⢄⠭⣐⠀⠂⢓⡀⣐⡈⠀⡀⠈⠀⢀⠁⠈⠀⡀⠀⡄⢘⠍⢄⠡⡤⎥
⎢⢰⠈⠰⡀⠀⠀⠄⡄⣀⢄⢀⠁⡄⡀⡀⡆⠒⢔⢈⠁⠄⢠⠀⠀⠄⠆⠂⣀⡄⠐⡀⢅⡐⡀⢁⢘⢰⠷⠐⠨⠀⠂⠀⣚⣀⣀⠀⢐⢀⠂⠂⠀⎥
⎢⠠⠐⠀⣀⡆⠂⣐⠄⡁⠰⠂⠀⠄⡀⡌⠢⠀⢠⢀⠐⠡⠐⠐⠃⡂⠕⠪⠢⡀⠐⠄⠄⣀⡀⠁⠠⢑⠀⢀⢐⠁⡃⡀⡔⡡⠀⡐⢀⠈⠀⡈⠂⎥
⎢⢠⠰⢀⠀⠤⢁⠄⠠⠀⠢⠐⠀⡤⠀⢔⡂⡈⠀⠆⠀⢂⠤⠅⠀⢄⢁⠀⠐⠠⢙⠔⡀⠀⠰⠀⠠⡠⠀⠀⠠⠀⡥⡠⠢⠂⠠⠚⠠⠈⠀⠆⢅⎥
⎢⠈⠀⢀⠂⢆⠢⠄⠀⠅⠐⡨⠡⠂⠡⠉⠄⡀⠙⠒⠈⠈⠐⠀⠂⠉⠥⢀⠬⠀⢈⠈⠅⠀⡉⠁⠉⠐⠩⠐⠙⠀⠒⠀⠁⢀⠀⢀⠠⠡⠀⢂⡀⎥
⎢⠥⡁⠠⢂⡁⡈⠙⢠⠐⠀⠐⠨⠁⡁⡂⠀⣄⠀⢀⢓⡀⢠⠉⡄⠈⡛⠘⣐⡀⢍⠀⡀⠀⡀⢀⠨⢐⢥⢉⢀⢀⠃⠃⠄⣀⢐⠀⢠⠠⠀⠂⠄⎥
⎢⢘⠢⠂⡀⡁⢄⠀⠀⡠⠀⠓⠐⠁⠂⢂⡁⡀⠀⠀⢓⣃⡀⠀⡀⡷⢃⠐⢘⠠⣀⠀⠐⠀⡉⣐⠨⠑⣠⠀⠐⢔⡂⠃⠍⢀⠐⣀⠀⠂⡁⠓⠀⎥
⎢⠢⢀⠀⠀⠀⠄⡢⠀⠰⠐⠀⠀⡖⠀⡁⠀⠊⠱⠴⠀⠀⡈⠁⠬⠂⠀⠀⠚⠐⠐⠀⠢⠂⠀⠤⠰⠀⠈⠀⢂⡐⡁⠐⠄⡄⠐⠈⠐⢀⠀⠀⡀⎥
⎣⢨⡄⠀⡐⡁⠔⠈⠈⢀⠡⠠⠄⠠⢁⡣⡁⠇⠢⠙⠀⡐⢀⠂⠡⠢⢠⠀⢠⢌⢉⠤⠣⠄⡠⠄⠃⠀⠈⢔⡠⡐⠀⠠⠆⠄⠘⠀⠍⠢⡌⠉⠀⎦
```
---
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [November 7, 2025, 5:01pm UTC](https://discourse.julialang.org/t/how-to-visualize-nans-in-an-array/133738/3 "2025-11-07T17:01:31Z")
Thank you a lot, it looks very nice!
Follow-up question: How can I check if any element of my array is NaN?
---
### Author:  [@mbauman](https://discourse.julialang.org/u/mbauman)
#### Post date: [November 7, 2025, 5:02pm UTC](https://discourse.julialang.org/t/how-to-visualize-nans-in-an-array/133738/4 "2025-11-07T17:02:02Z")
```julia-auto
julia> any(isnan, A)
true
```
---
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [November 7, 2025, 5:03pm UTC](https://discourse.julialang.org/t/how-to-visualize-nans-in-an-array/133738/5 "2025-11-07T17:03:20Z")
I have been using Julia for 12 years, and I still learn new functions every other week. 🙂
---
### Author:  [@mxhbl](https://discourse.julialang.org/u/mxhbl)
#### Post date: [November 7, 2025, 5:21pm UTC](https://discourse.julialang.org/t/how-to-visualize-nans-in-an-array/133738/6 "2025-11-07T17:21:46Z")
If you want to be extra fancy, you can also use `Plots.spy` with `UnicodePlots` for REPL output. 🙂
```julia-repl
julia> using UnicodePlots
julia> A = rand([0, NaN], 150, 150);
julia> spy(isnan.(A); width=60, height=30)
┌────────────────────────────────────────────────────────────┐
1 │⣛⣟⣭⣻⣹⣽⣟⢹⢹⣫⣽⣽⣼⣿⣢⡞⣎⣈⣛⠇⣭⡇⣞⣝⢋⣛⣫⣗⣿⣷⣩⣭⣾⣩⣻⣚⢽⣉⣻⡏⢫⣝⡞⢣⠹⡫⣕⢼⣏⢙⣭⣻⢿⠕⣩⢭⣥⡗⣏⠅│ > 0
│⡳⢫⣎⢌⣣⣫⢵⢼⢀⣾⣰⢶⡐⣫⣹⡗⣟⢚⣆⡍⣌⣟⠏⡙⣝⡏⢽⣾⢇⡗⣏⣭⣻⣋⣺⡧⣴⣩⢭⣝⣲⣃⣴⣝⣩⣥⣏⢚⣆⣑⡟⣩⡕⢵⣽⣃⣯⢀⣏⡄│ < 0
│⡫⣟⠔⣽⣤⣾⢚⢝⣋⡟⢂⣚⣣⣚⣣⡇⣑⢧⡯⣇⡻⣓⣷⣰⠈⣗⣢⣽⣐⣨⠿⣱⣑⢩⣫⣅⢔⡧⣑⣲⢛⣵⣩⣚⢛⣉⣧⣛⣖⢸⣒⣅⣗⣝⣟⡅⣗⡴⣿⡃│
│⣫⣺⣙⢿⣵⣺⣘⣽⡱⢏⣞⣹⠸⣶⢀⡖⣴⣮⠛⣟⢢⡮⣤⣪⣦⡏⣝⣦⣡⣐⣿⣩⣶⢒⣉⢍⣻⣷⣾⣼⡺⡽⢧⡵⣨⣅⡇⢼⣟⣼⣯⣟⣠⣟⡲⢸⡳⣁⡱⡃│
│⣿⣨⡇⢵⣃⣩⡴⣷⣞⢍⡌⢍⣔⣫⣁⣖⡢⡌⡽⠷⢳⣘⣾⣾⣹⣝⢋⣵⣶⣅⢾⡧⣓⠳⣻⠸⣞⡜⢏⡼⢽⣇⣶⣀⣗⣨⣖⣴⡇⣸⣣⡜⣛⢶⣞⣥⣷⣪⣏⠂│
│⣇⣖⣡⢞⡈⢹⣜⢛⡔⣚⣎⡪⠘⣠⣅⣿⡒⡥⣕⣌⢾⣶⡃⣿⣭⢯⡴⢧⣫⢗⣾⡷⢿⣑⣈⣣⣳⡴⣘⣫⣝⢫⣕⣌⢜⣒⡽⡡⡣⣫⡫⣵⣇⢆⣴⣡⣗⡻⣥⡇│
│⣷⢎⣐⣼⢌⣙⣘⢖⣉⣨⣫⢸⣳⣏⡂⣣⣘⡽⣹⡿⣄⣯⣮⣛⣺⡿⡭⣋⢷⣍⡦⣕⣙⠱⣻⣔⣩⡖⣮⠬⣾⢑⣾⢴⢝⣜⣵⣪⣏⣱⣱⡙⢿⢲⣏⢚⣯⢉⣷⡆│
│⢧⡸⣏⢽⠗⣱⣡⢭⠼⠼⠤⣵⡷⢮⡫⡿⠫⣮⢯⣆⡷⡿⠱⡿⡯⢕⢽⠟⠖⣇⢴⢬⣼⣢⢬⢾⡽⡭⣯⡡⢻⣾⢜⡜⡼⠮⡯⠧⢭⠿⣽⣭⣷⣟⡽⠘⡇⢩⣷⡆│
│⣿⢺⡶⣿⢧⡶⣠⠶⡅⢺⠕⡜⢡⣾⢾⣭⢾⠇⢪⣷⠯⡥⢩⡦⡼⣵⠍⢯⡍⡥⢺⠷⢾⠱⣷⠧⢿⠮⢻⠞⠮⣹⢽⠇⠽⡭⢷⠤⡯⢱⡿⣋⡷⠾⡦⠸⡦⡴⠦⡁│
│⣽⢺⠵⣶⠼⣫⠴⡰⣻⢴⡭⠬⠲⣴⣧⠌⢿⣭⠯⣟⡾⢯⠿⢦⢼⠥⣮⡷⣽⣷⣏⠼⢹⢭⣴⣆⣼⡶⢿⢬⢼⠡⣒⡶⡽⡥⠗⣠⡗⢆⣗⠷⣿⢵⠿⣇⣻⠖⢯⡄│
│⣽⢏⡜⢦⢵⡺⢇⡮⡭⣿⢝⢿⠅⣴⣦⡤⣭⣶⣲⠏⢭⠍⡤⠯⡰⣄⠼⢥⠎⠆⢼⣷⣼⠊⣷⠱⡥⢧⢳⢙⡽⠏⢸⣫⢯⣭⠍⢨⡷⣾⡗⡶⡷⢶⡿⣺⡬⠑⣗⠃│
│⢷⠿⢲⡾⢾⡽⢼⢞⡪⢸⣠⢭⢵⢼⢿⡤⡌⣧⣞⠖⣕⡧⢉⡟⢤⡧⡞⢍⢑⡭⢼⣇⠼⠦⣾⢗⡾⡂⢼⣥⡿⠯⢻⣾⣤⡔⡝⠿⢿⡯⣶⡻⡴⣲⢗⢤⡭⡷⡅⠅│
│⡧⢫⢒⠵⠬⠺⢣⢵⠟⢝⢘⡹⣢⡲⡿⣥⢦⡏⠼⡮⡢⣟⣤⡿⡸⠊⠗⣟⣭⠿⣨⣱⠾⡬⡵⠶⡾⠧⣾⢮⣤⠥⣯⢣⣽⡾⣵⠞⡯⣢⠶⠏⣿⢞⡷⢡⡧⠹⢥⠄│
│⡽⣬⣷⣿⠼⣽⣥⣹⠮⢯⣎⣖⠦⣽⣮⣵⠴⣇⡔⡿⠫⣏⣥⡿⡭⡴⣔⣾⣎⣿⡾⠵⢲⣼⡶⠭⡬⡄⡠⣴⣼⢢⢝⣬⣩⢯⡼⢡⡇⠴⡾⡞⢷⣯⡏⢫⡧⣜⣿⡅│
│⡵⣼⢮⢭⡝⢺⢯⢼⠧⢴⡵⣮⢤⢤⡊⡶⠮⣷⡬⠷⠷⢟⣴⢮⠝⡿⠴⣵⢵⡷⢸⢥⢵⣃⢵⡉⠶⢼⢻⠭⣾⡭⢬⣬⢝⠟⡯⠶⠿⢪⣟⢵⡗⣶⠥⠨⠿⠁⡭⠂│
│⣿⣳⢴⢙⣑⣩⢦⣲⡛⣾⢨⢷⢱⢚⢷⣗⣚⡟⣞⡿⡛⡳⣂⠖⠇⣷⠗⡷⣷⣓⡿⣛⡱⣚⢶⢚⡽⣲⣑⡿⣲⣟⡾⠦⢹⣢⢷⠒⢯⣖⡗⢼⣓⣳⣻⡻⣇⢷⠟⡆│
│⣛⣼⢐⢼⢒⢹⣬⣿⠗⣸⣟⣻⢿⢺⢚⣮⠒⡛⠟⡷⢌⣗⡝⢛⣟⣓⠵⠇⡰⡗⢾⢵⢻⢲⢶⡑⢺⠇⠴⠓⡿⣚⣕⡫⣯⣻⡞⣽⡷⡁⡗⡞⠮⡜⡟⢝⡷⠞⣷⡆│
│⣛⣺⢻⣴⣺⢶⠳⠻⡳⡳⡲⢹⠓⢻⣓⡛⢢⡟⠿⡗⣻⠗⠸⠳⢓⣿⣶⣖⠲⣟⢳⣻⡾⣶⢽⠖⢚⠽⢿⡲⢿⢾⢞⣟⢟⢦⣗⡞⡺⡔⠛⠨⣏⠳⣺⢲⡿⢰⣞⠆│
│⣥⢺⠗⡽⡏⢦⢟⣗⡞⢖⠳⢛⠃⣝⣷⣿⣾⠏⣛⣳⡵⣟⢻⣷⡹⡳⢿⠗⡳⡓⢽⣍⠺⣿⠲⢛⡺⡺⢻⢺⣹⡣⣚⢗⡿⣶⠷⣻⣚⣛⡦⡓⡼⠌⣣⠞⡗⠞⡓⡀│
│⡶⡿⢴⡿⢗⠮⣻⡛⢎⢾⠐⢻⣝⢺⡳⠿⢾⡿⢒⡿⣾⡟⢖⠗⠳⣦⢻⠯⢲⣧⢒⠿⣻⣪⢳⢯⡝⡰⢻⠊⢾⠪⣺⡓⣺⣪⣿⢾⡿⠍⡟⠷⢿⢕⣒⡝⣗⠷⣞⡆│
│⢗⣿⠷⢿⠒⠚⠵⣳⡒⠿⣞⡸⣓⢻⡛⠧⣗⣯⢽⡗⠻⣻⢔⢷⣧⡣⠴⣲⠏⠯⣺⣳⢷⡶⣙⣗⣾⢆⠘⢺⢙⡣⣟⡹⢽⠋⠇⠫⣝⠶⡯⣱⠜⣘⡓⢟⣗⠞⣏⠄│
│⡳⣻⢺⣽⡹⣞⣕⢟⡵⣹⢒⡻⡞⠞⠝⣚⣸⣞⡔⢳⠾⡾⣸⡝⣹⡗⣳⡎⣧⠏⢻⠰⣾⠇⡖⡒⡾⣝⠿⡟⠟⢣⣼⡑⢊⡗⢷⡊⣧⠮⣟⢸⢟⣾⡟⣾⡻⣲⡷⠅│
│⣟⡟⣳⣻⠂⢞⠖⡇⠵⣟⣹⣺⡊⠽⠍⠪⣋⡿⣺⣞⡗⣟⡃⣯⠚⡢⠃⡧⣎⡾⢻⣝⠻⠟⣐⢬⣻⠛⠾⢛⣺⣆⡸⡖⢛⢮⣻⣶⡶⢿⣆⡓⣂⡛⡟⠙⢿⢿⣏⡆│
│⡟⣿⣹⢺⣉⣯⠩⢯⢁⢿⡻⣿⠯⣛⠏⡏⠉⣿⣏⣝⣜⣟⣭⡷⠡⡯⡫⣯⡧⡷⢛⢭⣟⠃⢿⠋⢎⡭⡹⢩⣫⡭⣺⠙⢭⣿⡮⠍⣟⠸⠁⠫⡏⡤⡟⢺⣮⠋⣭⠅│
│⠗⣫⣹⢯⠿⣨⢗⠿⠍⢻⠫⣙⡱⠻⡭⡏⡫⡝⡛⣡⢪⣧⢜⣿⠀⠿⡟⣱⠻⣿⣛⢮⡭⠩⠍⠉⣾⡽⠼⣂⡺⠲⢿⡻⡟⣫⡝⢃⣭⡫⣏⡣⣭⠛⡧⣍⢳⢶⣭⡁│
│⡽⢟⡶⣝⣫⢻⡫⣿⠽⢯⠟⢿⠎⡩⠵⣍⠯⣛⡈⣻⡊⢝⢍⣑⠹⣳⡝⣕⡛⣧⢽⢨⡽⠞⠩⡓⣱⡅⢼⣉⢻⢟⣽⣹⠻⣓⡇⢳⢟⣬⣒⡾⡻⣋⢗⢁⣋⡄⠿⡇│
│⠟⡜⣙⠼⢳⡱⡿⣼⡛⢻⢃⡿⢮⣭⠜⡟⢊⡍⠙⠺⡷⣝⣺⡻⡙⠿⡭⠛⢹⣏⣌⣝⣼⡣⢻⣟⣭⡎⣌⣻⣮⠽⢛⠲⢻⣬⣮⠉⢧⡳⣉⣩⣟⠃⣍⢨⣏⣙⢏⡅│
│⡯⢿⢩⢋⠟⣝⠉⢲⠃⢵⡷⢿⠍⢭⣽⠫⡹⡯⣷⡗⢎⠏⢭⡏⠅⡫⢈⣭⡋⡫⣹⣳⣹⢌⣩⠏⣹⣝⠑⡙⢿⠩⢙⡿⡧⠉⡝⡚⣟⢚⣇⠏⣷⢙⢿⢷⣿⢥⡓⡃│
│⢙⣩⢃⣭⣚⣉⢽⡸⢋⢹⣯⠚⣭⣩⢫⣍⢵⣏⢫⣭⠂⡵⣩⣪⣿⣿⢩⣷⡢⡵⣏⡹⣽⢋⣹⣜⡕⢍⣹⢈⣩⠩⣟⣭⣫⠓⡹⢏⡝⡍⢙⠫⣮⠟⣏⡋⡿⠻⢍⠇│
150 │⠋⠹⠋⠫⠋⠹⠑⠙⠻⠑⠪⠿⠏⠽⠋⠇⠫⠿⠥⠉⠃⠻⠭⠁⠡⠏⠣⠁⠻⠝⠜⠭⠽⠮⠿⠍⠵⠹⠻⠉⠙⠣⠾⠝⠽⠾⠍⠯⠭⠩⠋⠇⠽⠏⠅⠏⠇⠈⠛⠁│
└────────────────────────────────────────────────────────────┘
⠀1⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀150⠀
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀11 223 ≠ 0⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
```
(The output even comes in color in my local REPL.)
---
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [November 7, 2025, 6:23pm UTC](https://discourse.julialang.org/t/how-to-visualize-nans-in-an-array/133738/7 "2025-11-07T18:23:35Z")
> [@mbauman](#):
>
> `sparse(isnan.(A))`
Using the following code now:
```julia-auto
if any(isnan, rel_vel)
println(" Warning: NaN values found in relative velocity field!")
display(sparse(isnan.(rel_vel)))
end
```
Key point: use `display`, not `println`.
Nice result:
```julia-auto
.DEBUG FlowField:
Warning: NaN values found in relative velocity field!
286×701 SparseArrays.SparseMatrixCSC{Bool, Int64} with 1144 stored entries:
⎡⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⢸⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⡇⠀⠀⠀⠀⠀⠀⠀⠀⎤
⎢⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⢸⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⡇⠀⠀⠀⠀⠀⠀⠀⠀⎥
⎢⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⢸⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⡇⠀⠀⠀⠀⠀⠀⠀⠀⎥
⎢⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⢸⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⡇⠀⠀⠀⠀⠀⠀⠀⠀⎥
⎢⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⢸⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⡇⠀⠀⠀⠀⠀⠀⠀⠀⎥
⎢⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⢸⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⡇⠀⠀⠀⠀⠀⠀⠀⠀⎥
⎢⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⢸⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⡇⠀⠀⠀⠀⠀⠀⠀⠀⎥
⎢⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⢸⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⡇⠀⠀⠀⠀⠀⠀⠀⠀⎥
⎢⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⢸⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⡇⠀⠀⠀⠀⠀⠀⠀⠀⎥
⎢⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⢸⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⡇⠀⠀⠀⠀⠀⠀⠀⠀⎥
⎢⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⢸⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⡇⠀⠀⠀⠀⠀⠀⠀⠀⎥
⎢⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⢸⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⡇⠀⠀⠀⠀⠀⠀⠀⠀⎥
⎢⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⢸⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⡇⠀⠀⠀⠀⠀⠀⠀⠀⎥
⎢⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⢸⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⠀⠀⠀⡇⠀⠀⠀⠀⠀⠀⠀⠀⎥
⎣⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠘⠀⠀⠀⠘⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠘⠀⠀⠀⠃⠀⠀⠀⠀⠀⠀⠀⠀⎦
```
---
### Author:  [@rafael.guerra](https://discourse.julialang.org/u/rafael.guerra)
#### Post date: [November 7, 2025, 7:04pm UTC](https://discourse.julialang.org/t/how-to-visualize-nans-in-an-array/133738/8 "2025-11-07T19:04:03Z")
Another REPL option, credit to @jd-foster ([this post](https://discourse.julialang.org/t/how-to-combine-prettytables-and-pager/85593/4)):
```julia
using PrettyTables, TerminalPager
A = rand(150, 150);
A[A .< .1] .= NaN;
hl = TextHighlighter((d, i, j) -> isnan(d[i,j]), crayon"red")
io = IOContext(IOBuffer(), :color => true);
pretty_table(io, A, alignment=:r, display_size=(-1,-1), show_row_number_column=true, highlighters=[hl])
pager(String(take!(io.io)), frozen_columns=7, frozen_rows=3)
```
