Apply Functions
tapply
The documentation definition for tapply is a bit more specific than the others, where the arguments are now (X, INDEX, FUN), with X being an object where the split function applies, INDEX is a factor by which X is grouped, and FUN is function as before.
To simplify this definition, we can say tapply applies FUN to X when X is grouped by INDEX.
Examples
Using the 1990 airport data, find the average arrival delay for flights arriving to each airport.
Click to see solution
# read in data
library(data.table)
myDF <- fread("/anvil/projects/tdm/data/flights/subset/1990.csv")
tapply(myDF$ArrDelay, myDF$Dest, mean, na.rm=TRUE)ABE
4.77494000685636
ABQ
7.7720134335519
ACY
5.58807588075881
AGS
8.35838529701346
ALB
7.51126007381186
AMA
8.567987065481
ANC
11.3615362811791
ATL
8.59703498508533
ATW
-11.2530120481928
AUS
6.21888427513992
AVL
5.56191744340879
AVP
7.23910171730515
AZO
3.33425245098039
BDL
7.50158685871726
BET
11.8017543859649
BFL
5.70559903672486
BGM
4.60901883052527
BGR
11.6194061062317
BHM
5.61821563433467
BIL
4.30690826727067
BIS
4.32569169960474
BLI
6.57166301969365
BNA
2.99054059116622
BOI
7.8021440958537
BOS
8.68138952412066
BTM
6.11143270622287
BTR
7.72758457534895
BTV
7.1847366117029
BUF
7.62385865053955
BUR
2.97791212264896
BWI
6.1178010854142
BZN
6.00830521671425
CAE
8.454398708636
CAK
5.69348127600555
CCR
1.0583596214511
CDV
8.37648809523809
CHA
4.97324001646768
CHO
1.20289855072464
CHS
6.19924840285607
CID
7.01145186335404
CLE
6.61321718321368
CLT
4.67219295572293
CMH
6.80954905153156
CMI
4.13047619047619
COS
6.41270635317659
CPR
2.16542750929368
CRP
8.06586538461539
CRW
4.07336780866193
CSG
9.57680872150644
CVG
6.96339948396139
DAB
8.97099236641221
DAL
6.65780198654277
DAY
4.34913098526703
DCA
4.99561621174524
DEN
8.17649503174869
DET
7.00324074074074
DFW
7.89527548306231
DLH
2.09291244788565
DRO
8.51226993865031
DSM
7.85462012320329
DTW
4.49481231688689
EFD
1.71490593342981
EGE
19.7676056338028
ELM
5.06831882116544
ELP
7.59123697568795
ERI
10.3340647284696
EUG
7.31041923551171
EVV
1.03066037735849
EWR
10.9039220458615
EYW
2.35234412759787
FAI
13.7152378067252
FAR
6.48727687048994
FAT
6.10478535159255
FAY
4.62673130193906
FCA
9.3623395149786
FLG
4.60611510791367
FLL
7.29924057150212
FNT
7.08815165876777
FSD
5.74075330844927
FWA
5.07532262312352
GCN
5.23130300693909
GEG
7.73432392273403
GFK
5.15888615888616
GJT
6.40649819494585
GNV
6.88170563961486
GPT
-2.19313725490196
GRB
2.87189942235814
GRR
6.03821780247636
GSO
5.93050173363247
GSP
5.2078535577207
GST
5.8433734939759
GTF
4.536172878171
GUC
12.8741935483871
GUM
6.95648994515539
HDN
12.9910554561717
HLN
5.77559912854031
HNL
8.48285796600403
HOU
7.46327180576008
HPN
7.09856850715746
HRL
6.3505170551011
HSV
5.29723702143477
HTS
0.164093767867353
IAD
3.77503405331777
IAH
7.52145911014401
ICT
5.33506746870428
IDA
5.31609498680739
ILM
2.90905688622754
IND
6.11051909071872
ISO
2.04705882352941
ISP
5.63258200476452
ITH
5.90425531914894
JAC
6.81378476420798
JAN
6.77225672877847
JAX
8.03287380699894
JFK
8.56741298292616
JNU
10.1031016657094
KOA
5.62354651162791
KTN
11.1808510638298
LAN
1.45423143350604
LAS
6.34067878021064
LAX
6.77925942712651
LBB
7.38479557069847
LEX
8.91636819484241
LFT
1.28228782287823
LGA
9.74154103691446
LGB
6.5527031349968
LIH
6.98290598290598
LIT
9.24171404798225
LNK
8.09978902953586
LSE
2.27272727272727
LYH
1.93421052631579
MAF
6.15070093457944
MBS
5.2624537432394
MCI
6.68386588116774
MCO
7.43624684439393
MDT
6.13469387755102
MDW
6.1485043251341
MEM
1.68064434055275
MFE
6.35710144927536
MFR
5.99726775956284
MGM
8.0270607826811
MHT
7.71730812514067
MIA
4.63792361554811
MKC
NaN
MKE
5.67506411847439
MLB
7.23610121168924
MLI
6.68748233964397
MLU
11.6878542510121
MOB
6.81279869448654
MOT
0.822210636079249
MRY
4.21257349615559
MSN
5.26094003241491
MSO
5.26537350392076
MSP
4.16160001569027
MSY
6.96222936666742
MYR
2.934493951018
OAJ
3.48700673724735
OAK
4.15983617898553
OGG
5.29461564510667
OKC
8.15177051413006
OMA
6.69852763697804
OME
9.19126819126819
ONT
6.90430555939131
ORD
7.27912239824301
ORF
5.77447365290829
ORH
5.24429530201342
OTZ
10.4608187134503
PBI
7.9410349881619
PDX
6.50698772886638
PHF
4.00297914597815
PHL
9.45196051685226
PHX
6.95228251756339
PIA
5.70398277717976
PIT
6.3972412263491
PMD
-1.02239789196311
PNS
5.30102461429749
PSC
8.78491620111732
PSE
30.5333333333333
PSG
10.7404958677686
PSP
5.7313654353562
PUB
1.26564344746163
PVD
6.60158940397351
PWM
9.11445259102771
RAP
4.07061143984221
RDM
23.8839285714286
RDU
2.72454148763647
RIC
5.67026798647996
RNO
7.14427173287277
ROA
4.29575200918485
ROC
7.98166175024582
ROP
6.25462962962963
ROR
14.1186868686869
RST
5.78303603931562
RSW
7.92674545738533
SAN
7.58327716365597
SAT
6.97933655072946
SAV
6.68496042216359
SBA
5.75875758991126
SBN
3.15600814663951
SCC
14.6488095238095
SCK
0.287528868360277
SDF
6.25623993558776
SEA
9.44925986737434
SFO
8.62202837723557
SGF
7.44886711573791
SHV
8.42518496149781
SIT
10.0407854984894
SJC
3.95574368504371
SJU
5.78930733379761
SLC
6.36349125734601
SMF
6.56662611516626
SNA
5.36249911152179
SPN
5.70601675552171
SRQ
7.5969014084507
STL
4.88090698355182
STT
3.57343234323432
STX
4.18855350842807
SUN
22.8157894736842
SUX
6.71904960400167
SWF
10.1408128219805
SYR
6.82989781536293
TLH
3.85142118863049
TOL
7.04215373715905
TPA
6.70032489299159
TRI
3.4688013136289
TUL
8.02563113454203
TUS
9.0590984795573
TVC
6.96660117878193
TVL
1.272614622057
TYS
6.53830949889548
UCA
1.56891495601173
VPS
1.17145593869732
WRG
8.79440789473684
YAK
7.70957613814757
YAP
23.2932330827068
YUM
3.88336402701044