Useful IDL Commands

I need to do some work for the likelihood project and thus code in IDL again. Because I am not working in IDL very frequently, I tend to forgot commands and syntax. I thought it would be useful to compile a list of commands here so that I don't have to keep looking these up again and again.

number of elements in an array:
print, N_ELEMENTS(array)

unix command in idl: dollar sign ($) before command
$pwd
$ls

list all variables currently being used:
help

doc_library, 'spherematch' -- man page for the function

which, 'spherematch' --- tells you where in the IDL path the function is.

when recompiling idlutils need to use evilmake

!pi is constant pi

plothist (makes histogram plot)

when looking at a structure you use the /str command:
help, mystructure, /str

reading a fits file using mrdfits:
filedata = mrdfits(file2read, 1)

Combine two structures of the same size:
struct3 =struct_combine(struct1,struct2)
Concatenate two structure of the same type:
struct3 = [struct1, struct2]

Plotting Histogram (from here):

PRO t_histogram
data = [[-5,  4,   2,  -8,  1], $
[ 3,  0,   5,  -5,  1], $
[ 6, -7,   4,  -4, -8], $
[-1, -5, -14,   2,  1]]
hist = HISTOGRAM(data)
bins = FINDGEN(N_ELEMENTS(hist)) + MIN(data)
PRINT, MIN(hist)
PRINT, bins
SPLOT, bins, hist, YRANGE = [MIN(hist)-1, MAX(hist)+1], PSYM = 10, XTITLE = 'Bin Number', YTITLE = 'Density per Bin'
END 

If you add maxmatch=1 to your spherematch it will avoid duplicates (should default to this)


total with higher precision: total(...., /double)


in for loops:
for j = 0L, rsize-1 do begin

the L makes j a long int.


;Show color table
colorName = PickColorName(startColorName)

; Make heat map (warning, not very sophisticated)


colorobject = qsotemplate1.z_sim
xobject = ugqcolor1
yobject = grqcolor1

colorbin = 0.3
colorstart = 1.0
colorstop = colorstart + colorbin

plot, xobject[0:1], yobject[0:1], ps=null, color=fsc_color('white'), xr=[-0.5,4],yr=[-0.5,2], XTITLE = 'u-g magnitude', YTITLE = 'g-r magnitude', TITLE = 'Color-Color Diagram QSO Catalog Jiang Combo', charsize = 1.5, charthick = 1

zrange = where(colorobject GE colorstart AND colorobject LT colorstop)
oplot, xobject[zrange], yobject[zrange], ps=3, color=FSC_COLOR('dark red') ;Fake QSOs
colorstart = colorstop
colorstop = colorstart + colorbin
zrange = where(colorobject GE colorstart AND colorobject LT colorstop)
oplot, xobject[zrange], yobject[zrange], ps=3, color=FSC_COLOR('red') ;Fake QSOs
colorstart = colorstop
colorstop = colorstart + colorbin
zrange = where(colorobject GE colorstart AND colorobject LT colorstop)
oplot, xobject[zrange], yobject[zrange], ps=3, color=FSC_COLOR('orange red') ;Fake QSOs
colorstart = colorstop
colorstop = colorstart + colorbin
zrange = where(colorobject GE colorstart AND colorobject LT colorstop)
oplot, xobject[zrange], yobject[zrange], ps=3, color=FSC_COLOR('orange') ;Fake QSO
colorstart = colorstop
colorstop = colorstart + colorbin
zrange = where(colorobject GE colorstart AND colorobject LT colorstop)
oplot, xobject[zrange], yobject[zrange], ps=3, color=FSC_COLOR('gold') ;Fake QSOs
colorstart = colorstop
colorstop = colorstart + colorbin
zrange = where(colorobject GE colorstart AND colorobject LT colorstop)
oplot, xobject[zrange], yobject[zrange], ps=3, color=FSC_COLOR('lawn green') ;Fake QSOs
colorstart = colorstop
colorstop = colorstart + colorbin
zrange = where(colorobject GE colorstart AND colorobject LT colorstop)
oplot, xobject[zrange], yobject[zrange], ps=3, color=FSC_COLOR('lime green') ;Fake QSOs
colorstart = colorstop
colorstop = colorstart + colorbin
zrange = where(colorobject GE colorstart AND colorobject LT colorstop)
oplot, xobject[zrange], yobject[zrange], ps=3, color=FSC_COLOR('dark green') ;Fake QSOs
colorstart = colorstop
colorstop = colorstart + colorbin
zrange = where(colorobject GE colorstart AND colorobject LT colorstop)
oplot, xobject[zrange], yobject[zrange], ps=3, color=FSC_COLOR('teal') ;Fake QSOs
colorstart = colorstop
colorstop = colorstart + colorbin
zrange = where(colorobject GE colorstart AND colorobject LT colorstop)
oplot, xobject[zrange], yobject[zrange], ps=3, color=FSC_COLOR('dodger blue') ;Fake QSOs
colorstart = colorstop
colorstop = colorstart + colorbin
zrange = where(colorobject GE colorstart AND colorobject LT colorstop)
oplot, xobject[zrange], yobject[zrange], ps=3, color=FSC_COLOR('royal blue') ;Fake QSOs
colorstart = colorstop
colorstop = colorstart + colorbin
zrange = where(colorobject GE colorstart AND colorobject LT colorstop)
oplot, xobject[zrange], yobject[zrange], ps=3, color=FSC_COLOR('blue') ;Fake QSOs
colorstart = colorstop
colorstop = colorstart + colorbin
zrange = where(colorobject GE colorstart AND colorobject LT colorstop)
oplot, xobject[zrange], yobject[zrange], ps=3, color=FSC_COLOR('navy') ;Fake QSOs
colorstart = colorstop
colorstop = colorstart + colorbin
zrange = where(colorobject GE colorstart AND colorobject LT colorstop)
oplot, xobject[zrange], yobject[zrange], ps=3, color=FSC_COLOR('dark slate blue') ;Fake QSOs
colorstart = colorstop
colorstop = colorstart + colorbin
zrange = where(colorobject GE colorstart AND colorobject LT colorstop)
oplot, xobject[zrange], yobject[zrange], ps=3, color=FSC_COLOR('dark orchid') ;Fake QSOs

The hope is that I will expand on this list every time I come across something I think I might use again (but don't use enough to memorize).